Golf ball with multi-layer cover utilizing polyurethane materials

ABSTRACT

A golf ball is described having a core with a multi-layer cover that includes one or more polyurethane materials and which exhibits a Shore D hardness of at least 60. The one or more polyurethane materials may be utilized in one, all, or in only some of the individual cover layers that form the multi-layer cover.

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This is a continuation-in-part of U.S. application Ser. No. 09/335,302 filed Jun. 17, 1999, which is a continuation-in-part of U.S. application Ser. No. 08/743,579 filed Nov. 4, 1996 and issued as U.S. Pat. No. 5,833,553, which is a continuation-in-part of U.S. application Ser. No. 08/240,259 filed May 10, 1994 now abandoned, which in turn is a continuation-in-part of U.S. application Ser. No. 08/054,406, filed Apr. 28, 1993, which issued as U.S. Pat. No. 5,368,304.

FIELD OF THE INVENTION

[0002] The present invention relates generally to golf balls, and more particularly to golf balls having multi-layer covers that utilize one or more polyurethane materials. Preferably, the cover layers exhibit hardnesses less than 60 as measured on the Shore D hardness scale. In a further aspect, the present invention relates to golf balls having multi-layer covers in which each of the individual cover layers have the same, or similar, hardness.

BACKGROUND OF THE INVENTION

[0003] Top grade golf balls sold in the United States generally comprise a central core with one or more cover layers formed thereover. A golf ball cover is particularly influential in effecting the compression (feel) and durability (i.e., impact resistance, etc.) of the resulting ball. Various cover compositions have been developed in order to optimize desired properties of the resulting golf balls.

[0004]FIGS. 1 and 2 illustrate a conventional golf ball 10 having a single cover layer 14 molded about a golf ball core 16. FIG. 2 illustrates (in an exaggerated view) stress lines 12 extending partially, or entirely across the thickness of the cover layer 14. Stress lines 12 typically result in a crack or fracture across the thickness of the golf ball cover. FIGS. 1 and 2 illustrate one problem that may occur when a very thick, single layer cover is formed about a golf ball core.

[0005] Although not wishing to be bound to any particular theory, it is believed that stress lines in a golf ball cover, such as stress lines 12 in cover 14, result from repeated strikes with a golf club, particularly drivers, and temperature effects. Stress lines often serve as initiation sites for crack or fracture propagation in a golf ball cover material. Such cracks or fractures, and their related stress lines, are undesirable in golf ball covers. Moreover, it is particularly undesirable for such stress lines and the resulting cracks or fractures to extend across the entire thickness of a golf ball cover since such damage significantly impairs golf ball performance. And, such cracks or fractures greatly reduce the durability of a golf ball cover.

[0006] When a multi-layer cover is employed, each cover layer traditionally has had a significantly different Shore D hardness than an adjacent cover layer in order to impart to the golf ball a particular desired combination of spin and distance characteristics. Although the use of a multi-layer cover configuration reduces the tendency of stress lines, and thus cracks and fractures, propagating across the entire thickness of the cover, such multi-layer arrangement of cover materials, each having its own particular set of properties and characteristics, has associated design and manufacturing problems.

[0007] For instance, in order to produce a multiple cover layer golf ball that exhibits a desired set of performance characteristics, it is necessary to design and anticipate an overall performance profile for the set of cover layers. This involves analyzing each of the individual cover layers and any and all effects between the individual cover layers. Even if such daunting design analysis is performed, the increased number of variables may lead to unanticipated difficulties in manufacturing or with the final product golf ball.

[0008] In addition, although, once again, not wishing to be bound to any particular theory, it is believed that although a multiple cover layer configuration may reduce the tendency for cracks or fractures that extend through the entire thickness of the cover, such configuration may lead to an increase in the number or frequency of fractures, particularly in applications in which the various cover layers constituting the multi-layer cover each have different physical properties such as hardness and flexural characteristics.

[0009] Accordingly, there is a need for an improved golf ball which is less susceptible to cracking or fracturing across the thickness of the cover than currently known single cover layer golf balls. And, there is a need for an improved multiple cover layer golf ball that is simpler to design and manufacture, and which is less susceptible to cracking or fracturing of one or more of the individual cover layers that constitute the multiple cover layer of the ball.

BRIEF SUMMARY OF THE INVENTION

[0010] The present invention relates to new and improved golf balls which overcome the above-referenced problems and others. In a first aspect, the present invention provides a golf ball comprising a core, a first cover layer disposed about the core, and a second outermost cover layer disposed on the first cover layer. The first inner cover layer comprises a majority proportion by weight of a polyurethane. The first cover layer exhibits a Shore D hardness of less than 60. The second outermost cover layer comprises a majority proportion by weight of a polyurethane, and exhibits a Shore D hardness of less than 60.

[0011] In another aspect, the present invention provides a golf ball comprising a core, a first cover layer disposed about the core, and a second outermost cover layer disposed on the first cover layer. The first inner cover layer comprises a majority proportion by weight of a polyurethane and exhibits a Shore D hardness less than 60. The second outermost cover layer exhibits a Shore D hardness less than 60.

[0012] In yet another aspect, the present invention provides a golf ball comprising a core, a first cover layer disposed about the core, and a second outermost cover layer disposed on the first inner cover layer. The inner cover layer exhibits a Shore D hardness of less than 60. And, the second outermost cover layer exhibits a Shore D hardness of less than 60. Furthermore, the second outermost cover layer comprises a majority proportion by weight of a polyurethane.

[0013] Other features and objectives of the present invention will be pointed out in more detail hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014] The following is a brief description of the drawings which are presented for the purposes of illustrating the invention and not for the purposes of limiting the same.

[0015]FIG. 1 is a perspective view of a conventional single cover layer golf ball.

[0016]FIG. 2 is a partial cross sectional view of the golf ball depicted in FIG. 1, taken across line 2-2, illustrating stress lines extending partially or entirely across the thickness of the golf ball cover.

[0017]FIG. 3 is a partial cross section of a preferred embodiment solid golf ball with a dual layer cover according to the present invention.

[0018]FIG. 4 is a partial cross section of a preferred embodiment solid golf ball with a three layer cover according to an alternative embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] The present invention generally provides a golf ball having a multiple layer cover in which one or more properties of each of the individual cover layers are matched so that certain desired properties are the same, or substantially so. In several of the preferred embodiments described herein, the individual cover layers all have the same, or nearly the same, Shore D hardness. The present invention includes matching of one or more further properties or characteristics of individual cover layers in a multiple cover layer assembly utilized in a golf ball. The present invention is embodied in golf balls having multi-layer cover assemblies comprising two, three, or more cover layers.

[0020] In a particularly preferred aspect, the golf ball of the present invention has a solid core having a coefficient of restitution (COR) of at least about 0.650 in combination with a thick, relatively soft cover assembly which is formed from two or more layers. Each cover layer has a Shore D hardness within 5 points, and preferably within 2 points, of the Shore D hardness of all other cover layers.

[0021] Referring to the drawings and particularly to FIG. 3, a first preferred embodiment of a golf ball according to the present invention is shown and is designated as 20. The golf ball 20 has a core 26. The core 26 can consist of a solid or wound core and can consist of one or more layers.

[0022] A multi-layer cover surrounds the core 26. The multi-layer cover includes a non-dimpled inner cover layer 24 and a dimpled outer cover layer 22. The outer cover layer 22 defines a plurality of dimples 27 and an outer surface 28 to form an unfinished golf ball.

[0023] A thin primer coat (not shown) is preferably applied to the outer surface of cover layer 22. A thin top coat (not shown) also preferably surrounds the primer coat to form a finished ball. Optionally, one or more pigmented paint coat(s) can be substituted for the primer coat and/or top coat. In one preferred embodiment, the core 26 is relatively soft, with a PGA compression of about 85 or less, preferably about 20 to 85, and more preferably about 40 to 60. PGA compression is described and defined herein below.

[0024] The multi-layer cover has an overall cover thickness of at least about 3.6 mm (0.142 inches). It is particularly preferred that the cover thickness be at least 3.8 mm (0.150 inches). Particularly good results are obtained when the cover has a thickness of at least 4.0 mm (0.157 inches). In certain circumstances, such as when a harder compression and harder feel may be desired, it is useful to employ a cover having a thickness of at least 4.5 mm (0.177 inches). The thickness of the individual cover layers may vary depending upon the thicknesses of the other cover layers and the desired overall cover layer thickness. It may, in some applications, be desirable to form the outermost cover layer to be relatively thick due to the presence of the dimples.

[0025] As used herein, “overall cover thickness” is the thickness of the multi-layer cover as measured from the inner diameter of the innermost cover to the outer surface of the outermost or exterior cover at a land (i.e. non-dimpled) area. The “cover layer thickness” of any particular cover layer is the thickness of the layer from its inner diameter to its outer surface. If the outer surface of the layer is dimpled, the measurement is made to a land area of the cover layer.

[0026] The preferred golf ball of the present invention preferably exhibits a difference between the coefficient of restitution of the ball and the coefficient of restitution of the core of at least about 0.025, preferably at least 0.035, and more preferably at least 0.045. The golf balls exhibit an unexpectedly long distance upon impact or drives given their coefficient of restitution.

[0027] In one preferred embodiment, each layer of the multi-layer cover assembly has a Shore D hardness of less than 60, more preferably less than 55, and most preferably less than 50.

[0028] The golf balls of the present invention can be produced by molding processes currently well known in the golf ball art. Specifically, the golf balls can be produced by injection molding or compression molding the cover compositions described herein about wound or solid molded cores to produce a golf ball having a diameter of about 1.680 to about 1.800 inches and weighing about 1.620 ounces. The standards for both the minimum diameter and maximum weight of the balls have been established by the United States Golf Association (U.S.G.A.).

[0029] Although both solid core and wound cores can be utilized in the present invention, as a result their lower cost and superior performance, solid molded cores are preferred over wound cores.

[0030] The term “solid cores” as used herein refers not only to one piece cores but also to those cores having a separate solid layer beneath the cover and above the core as in U.S. Pat. No. 4,431,193, and other multi-layer and/or non-wound cores. The compositions of suitable cores that can be incorporated into the present invention are presented in more detail below.

[0031] The layers of the multi-layer cover may be formed from generally the same resin composition, or may be formed from different resin compositions with similar hardnesses. For example, one cover layer may be formed from an ionomeric resin of ethylene and methacrylic acid, while another layer is formed from an ionomer of ethylene and acrylic acid. One or more cover layers may contain polyamides or polyamide-nylon copolymers or intimate blends thereof. Furthermore, polyurethanes, Pebax® polyetheramides, Hytrel® polyesters, and/or thermosetting polyurethanes can be used. In order to visibly distinguish the layers, various colorants, metallic flakes, phosphorous, florescent dyes, florescent pigments, etc. can be incorporated in the resin. Preferably, the various cover layers that comprise ionomer are made of at least 50 weight % ionomer based upon 100 parts by weight of resin composition, and more preferably 75 or more weight % ionomer. However, as explained in greater detail herein, it is preferred that at least one of the cover layers of the multi-layer cover comprise a polyurethane, and most preferably, at least 50% by weight. Additional description and details of suitable materials for cover layers are provided herein.

[0032] Preferable cover materials for use as inner or outer cover layers include, for example, zinc, sodium and lithium ionomers, and blends of ionomers with harder non-ionic polymers such as nylon, polyphenylene oxide, metallocene catalyzed polyolefins, and other compatible thermoplastics. A wide array of nylon materials or blends thereof can be incorporated in the present invention golf ball covers. This is described in greater detail herein. Moreover, various suitable ionomers are further described below. Furthermore, examples of cover compositions which may be used are set forth in detail in copending U.S. application Ser. No. 08/596,690, which is a continuation of U.S. application Ser. No. 08/174,765 now abandoned, which in turn is a continuation of U.S. Ser. No. 07/776,803 filed Oct. 15, 1991 now abandoned, and U.S. application Ser. No. 08/493,089 issued as U.S. Pat. No. 5,688,869, which is a continuation of Ser. No. 07/981,751 now abandoned, which in turn is a continuation of U.S. application Ser. No. 07/901,660 filed Jun. 19, 1992 now abandoned, all of which are incorporated herein by reference. The cover compositions are not limited in any way to the compositions set forth in said copending applications.

[0033] A further embodiment of a golf ball according to the present invention is shown in FIG. 4, and is designated as golf ball 30. The ball 30 has a core 38, as is illustrated in FIG. 3. The core 38 preferably has a PGA compression of about 85 or less, preferably 20 to 85, and more preferably 40 to 60.

[0034] A multi-layer cover having three layers is formed over the core 38 to produce an unfinished golf ball. In the embodiment shown, the cover includes an inner cover layer 36, an intermediate inner cover layer 34 and an outer cover layer 32. Again, as in the embodiment illustrated in FIG. 3, further finished coat(s) (not shown) can be included to produce a finished golf ball. The inner, intermediate, and outer cover layers 36, 34 and 32 respectively, preferably exhibit substantially the same Shore D hardness. Restated, the difference between the Shore D hardness of any two of these cover layers is preferably 5 or less, and most preferably is 2 or less. Preferably, each of the cover layers 36, 34 and 32 has a Shore D hardness of less than 60, more preferably less than 55, and most preferably less than 50.

[0035] The overall thickness of the multi-layer cover assembly shown in FIG. 4 can be the same as the thickness of the multi-layer cover assembly of the embodiment of FIG. 3. The thickness of the individual cover layers may vary depending upon the thicknesses of the other cover layers and the desired overall cover layer thickness. It may, in some applications, be desirable to form the outermost cover layer to be relatively thick due to the presence of the dimples. The three cover layers 36, 34 and 32 can be formed from the same or different resin compositions, and preferably comprise ionomer, ionomer blends, polyurethanes, polyureas, polyurethane blends, etc.

[0036] A detailed description of the various components and materials utilized in the present invention golf balls is set forth below after a description of various golf ball properties and their measurement. Moreover, further multiple cover layers are also included as being within the scope of the present invention.

[0037] As used herein, “Shore D hardness” of a cover is measured generally in accordance with ASTM D-2240, except the measurements are made on the curved surface of a molded cover, rather than on a plaque. Furthermore, the Shore D hardness of the cover is measured while the cover remains over the core. When a hardness measurement is made on a dimpled cover, Shore D hardness is measured at a land area of the dimpled cover.

[0038] Two principal properties involved in golf ball performance are resilience and PGA compression. Resilience is determined by the coefficient of restitution (C.O.R.), i.e. the constant “e” which is the ratio of the relative velocity of an elastic sphere after direct impact to that before impact. As a result, the coefficient of restitution (“e”) can vary from 0 to 1, with 1 being equivalent to a perfectly or completely elastic collision and 0 being equivalent to a perfectly or completely inelastic collision.

[0039] Resilience (C.O.R.), along with additional factors such as club head speed, angle of trajectory and ball configuration (i.e., dimple pattern) generally determine the distance a ball will travel when hit. Since club head speed and the angle of trajectory are factors not easily controllable by a manufacturer, factors of concern among manufacturers are the coefficient of restitution (C.O.R.) and the surface configuration of the ball.

[0040] The coefficient of restitution (C.O.R.) in solid core balls is a function of the composition of the molded core and of the cover. In balls containing a wound core (i.e., balls comprising a liquid or solid center, elastic windings, and a cover), the coefficient of restitution is a function of not only the composition of the center and cover, but also the composition and tension of the elastomeric windings.

[0041] The coefficient of restitution is the ratio of the outgoing velocity to the incoming velocity. In the examples of this application, the coefficient of restitution of a golf ball was measured by propelling a ball horizontally at a speed of 125±1 feet per second (fps) against a generally vertical, hard, flat steel plate and measuring the ball's incoming and outgoing velocity electronically. Speeds were measured with a pair of Ohler Mark 55 ballistic screens, which provide a timing pulse when an object passes through them. The screens are separated by 36 inches and are located 25.25 inches and 61.25 inches from the rebound wall. The ball speed was measured by timing the pulses from screen 1 to screen 2 on the way into the rebound wall (as the average speed of the ball over 36 inches), and then the exit speed was timed from screen 2 to screen 1 over the same distance. The rebound wall was tilted 2 degrees from a vertical plane to allow the ball to rebound slightly downward in order to miss the edge of the cannon that fired it.

[0042] As indicated above, the incoming speed should be 125+/−1 fps. Furthermore, the correlation between COR and forward or incoming speed has been studied and a correction has been made over the +/−1 fps range so that the COR is reported as if the ball had an incoming speed of exactly 125.0 fps.

[0043] The coefficient of restitution must be carefully controlled in all commercial golf balls if the ball is to be within the specifications regulated by the United States Golf Association (U.S.G.A.). Along this line, the U.S.G.A. standards indicate that a “regulation” ball cannot have an initial velocity (i.e., the speed off the club) exceeding 255 feet per second in an atmosphere of 75° F. when tested on a U.S.G.A. machine. Since the coefficient of restitution of a ball is related to the ball's initial velocity, it is highly desirable to produce a ball having sufficiently high coefficient of restitution to closely approach the U.S.G.A. limit on initial velocity, while having an ample degree of softness (i.e., hardness) to produce enhanced playability (i.e., spin, etc.).

[0044] As indicated above, PGA compression is another important property involved in the performance of a golf ball. The compression of the ball can affect the playability of the ball on striking and the sound or “click” produced. Similarly, compression can effect the “feel” of the ball (i.e., hard or soft responsive feel), particularly in chipping and putting.

[0045] Moreover, while compression itself has little bearing on the distance performance of a ball, compression can affect the playability of the ball on striking. The degree of compression of a ball against the club face and the softness of the cover strongly influences the resultant spin rate. Typically, a softer cover will produce a higher spin rate than a harder cover. Additionally, a harder core will produce a higher spin rate than a softer core. This is because at impact a hard core serves to compress the cover of the ball against the face of the club to a much greater degree than a soft core thereby resulting in more “grab” of the ball on the clubface and subsequent higher spin rates. In effect the cover is squeezed between the relatively incompressible core and clubhead. When a softer core is used, the cover is under much less compressive stress than when a harder core is used and therefore does not contact the clubface as intimately. This results in lower spin rates.

[0046] The term “compression” utilized in the golf ball trade generally defines the overall deflection that a golf ball undergoes when subjected to a compressive load. For example, PGA compression indicates the amount of change in golf ball's shape upon striking. The development of solid core technology in two-piece balls has allowed for much more precise control of compression in comparison to thread wound three-piece balls. This is because in the manufacture of solid core balls, the amount of deflection or deformation is precisely controlled by the chemical formula used in making the cores. This differs from wound three-piece balls wherein compression is controlled in part by the winding process of the elastic thread. Thus, two-piece and multi-layer solid core balls exhibit much more consistent compression readings than balls having wound cores such as the thread wound three-piece balls.

[0047] In the past, PGA compression related to a scale of from 0 to 200 given to a golf ball. The lower the PGA compression value, the softer the feel of the ball upon striking. In practice, tournament quality balls have compression ratings around 50 to 110, and preferably around 80 to 100.

[0048] In determining PGA compression using the 0 to 200 scale, a standard force is applied to the external surface of the ball. A ball which exhibits no deflection (0.0 inches in deflection) is rated 200 and a ball which deflects {fraction (2/10)}th of an inch (0.2 inches) is rated 0. Every change of 0.001 of an inch in deflection represents a 1 point drop in compression. Consequently, a ball which deflects 0.1 inches (100×0.001 inches) has a PGA compression value of 100 (i.e., 200 to 100) and a ball which deflects 0.110 inches (110×0.001 inches) has a PGA compression of 90 (i.e., 200 to 110).

[0049] In order to assist in the determination of compression, several devices have been employed by the industry. For example, PGA compression is determined by an apparatus fashioned in the form of a small press with an upper and lower anvil. The upper anvil is at rest against a 200-pound die spring, and the lower anvil is movable through 0.300 inches by means of a crank mechanism. In its open position the gap between the anvils is 1.780 inches allowing a clearance of 0.100 inches for insertion of the ball. As the lower anvil is raised by the crank, it compresses the ball against the upper anvil, such compression occurring during the last 0.200 inches of stroke of the lower anvil, the ball then loading the upper anvil which in turn loads the spring. The equilibrium point of the upper anvil is measured by a dial micrometer if the anvil is deflected by the ball more than 0.100 inches (less deflection is simply regarded as zero compression) and the reading on the micrometer dial is referred to as the compression of the ball. In practice, tournament quality balls have compression ratings around 80 to 100 which means that the upper anvil was deflected a total of 0.120 to 0.100 inches.

[0050] An example to determine PGA compression can be shown by utilizing a golf ball compression tester produced by Atti Engineering Corporation of Newark, N.J. The value obtained by this tester relates to an arbitrary value expressed by a number which may range from 0 to 100, although a value of 200 can be measured as indicated by two revolutions of the dial indicator on the apparatus. The value obtained defines the deflection that a golf ball undergoes when subjected to compressive loading. The Atti test apparatus consists of a lower movable platform and an upper movable spring-loaded anvil. The dial indicator is mounted such that it measures the upward movement of the spring-loaded anvil. The golf ball to be tested is placed in the lower platform, which is then raised a fixed distance. The upper portion of the golf ball comes in contact with and exerts a pressure on the spring-loaded anvil. Depending upon the distance of the golf ball to be compressed, the upper anvil is forced upward against the spring.

[0051] Alternative devices have also been employed to determine compression. For example, Applicant also utilizes a modified Riehle Compression Machine originally produced by Riehle Bros. Testing Machine Company, Philadelphia, Pa. to evaluate compression of the various components (i.e., cores, mantle cover balls, finished balls, etc.) of the golf balls. The Riehle compression device determines deformation in thousandths of an inch under a load designed to emulate the 200 pound spring constant of the Atti or PGA compression testers. Using such a device, a Riehle compression of 61 corresponds to a deflection under load of 0.061 inches.

[0052] Additionally, an approximate relationship between Riehle compression and PGA compression exists for balls of the same size. It has been determined by Applicant that Riehle compression corresponds to PGA compression by the general formula PGA compression equals 160 minus Riehle compression. Consequently, 80 Riehle compression corresponds to 80 PGA compression, 70 Riehle compression corresponds to 90 PGA compression, and 60 Riehle compression corresponds to 100 PGA compression. For reporting purposes, Applicant's compression values are usually measured as Riehle compression and converted to PGA compression.

[0053] Furthermore, additional compression devices may also be utilized to monitor golf ball compression so long as the correlation to PGA compression is known. These devices have been designed, such as a Whitney Tester, to correlate or correspond to PGA compression through a set relationship or formula.

Core

[0054] The core which is used to form the golf balls of the present invention can be solid, foamed, wound, hollow or liquid. The core can be unitary, or can have two or more core layers. A solid core or solid layer of a multi-layer core can be thermosetting or thermoplastic. Preferably, the core is solid and is formed from a thermoset material.

[0055] Solid cores of the more preferred embodiment of the present invention can be manufactured using relatively conventional techniques. In this regard, the core compositions of the invention may be based on polybutadiene, natural rubber, metallocene catalyzed polyolefins such as Exact® (Exxon Chem. Co.) and Engage® (Dow Chem. Co.), polyurethanes, other thermoplastic or thermoset elastomers, and mixtures of one or more of the above materials with each other and/or with other elastomers. The core may be formed from a uniform composition or may be a dual or multi-layer core. The core may be foamed or unfoamed.

[0056] It is preferred that the base elastomer have a relatively high molecular weight. Polybutadiene has been found to be particularly useful because it imparts to the golf balls a relatively high coefficient of restitution. Polybutadiene can be cured using a free radical initiator such as a peroxide, or can be sulfur cured. A broad range for the molecular weight of preferred base elastomers is from about 50,000 to about 500,000. A more preferred range for the molecular weight of the base elastomer is from about 100,000 to about 500,000. As a base elastomer for the core composition, cis-1-4-polybutadiene is preferably employed, or a blend of cis-1-4-polybutadiene with other elastomers may also be utilized. Most preferably, cis-1-4-polybutadiene having a weight-average molecular weight of from about 100,000 to about 500,000 is employed. Along this line, it has been found that the high cis-1-4-polybutadienes manufactured and sold by Bayer Corp., Germany, under the trade name Taktene® 220 or 1220 are particularly preferred. Furthermore, the core may be comprised of a crosslinked natural rubber, EPDM, metallocene catalyzed polyolefin, or another crosslinkable elastomer.

[0057] When polybutadiene is used for golf ball cores, it commonly is crosslinked with an unsaturated carboxylic acid co-crosslinking agent. The unsaturated carboxylic acid component of the core composition typically is the reaction product of the selected carboxylic acid or acids and an oxide or carbonate of a metal such as zinc, magnesium, barium, calcium, lithium, sodium, potassium, cadmium, lead, tin, and the like. Preferably, the oxides of polyvalent metals such as zinc, magnesium and cadmium are used, and most preferably, the oxide is zinc oxide.

[0058] Exemplary of the unsaturated carboxylic acids which find utility in the core compositions are acrylic acid, methacrylic acid, itaconic acid, crotonic acid, sorbic acid, and the like, and mixtures thereof. Preferably, the acid component is either acrylic or methacrylic acid. Usually, from about 5 to about 40, and preferably from about 15 to about 30 parts by weight of the carboxylic acid salt, such as zinc diacrylate, is included in the core composition. The unsaturated carboxylic acids and metal salts thereof are generally soluble in the elastomeric base, or are readily dispersible.

[0059] The free radical initiator included in the core composition is any known polymerization initiator (a co-crosslinking agent) which decomposes during the cure cycle. The term “free radical initiator” as used herein refers to a chemical which, when added to a mixture of the elastomeric blend and a metal salt of an unsaturated, carboxylic acid, promotes crosslinking of the elastomers by the metal salt of the unsaturated carboxylic acid. The amount of the selected initiator present is dictated only by the requirements of catalytic activity as a polymerization initiator. Suitable initiators include peroxides, persulfates, azo compounds and hydrazides. Peroxides which are readily commercially available are conveniently used in the present invention, generally in amounts of from about 0.1 to about 10.0 and preferably in amounts of from about 0.3 to about 3.0 parts by weight per each 100 parts of elastomer.

[0060] Exemplary of suitable peroxides for the purposes of the present invention are dicumyl peroxide, n-butyl 4,4′-bis (butylperoxy) valerate, 1,1-bis(t-butylperoxy)-3,3,5-trimethyl cyclohexane, di-t-butyl peroxide and 2,5-di-(t-butylperoxy)-2,5 dimethyl hexane and the like, as well as mixtures thereof. It will be understood that the total amount of initiators used will vary depending on the specific end product desired and the particular initiators employed.

[0061] Examples of such commercially available peroxides are Luperco® 230 or 231 XL sold by Atochem, Lucidol Division, Buffalo, N.Y., and Trigonox® 17/40 or 29/40 sold by Akzo Chemicals, America, Chicago, Ill. In this regard Luperco® 230 XL and Trigonox® 29/40 are comprised of 1,1-bis(t-butylperoxy)-3,3,5-trimethyl cyclohexane. The one hour half life of Luperco® 231 XL is about 112° C., and the one hour half life of Trigonox® 29/40 is about 129° C.

[0062] The core compositions of the present invention may additionally contain any other suitable and compatible modifying ingredients including, but not limited to, metal oxides, fatty acids, and diisocyanates and polypropylene powder resin. For example, Papi® 94, a polymeric diisocyanate, commonly available from Dow Chemical Co., Midland, Mich., is an optional component in the rubber compositions. It can range from about 0 to 5 parts by weight per 100 parts by weight rubber (phr) component, and acts as a moisture scavenger. In addition, it has been found that the addition of a polypropylene powder resin results in a core which is hard (i.e. exhibits high PGA compression) and thus allows for a reduction in the amount of crosslinking co-agent utilized to soften the core to a normal or below normal compression.

[0063] Furthermore, because polypropylene powder resin can be added to a core composition without an increase in weight of the molded core upon curing, the addition of the polypropylene powder allows for the addition of higher specific gravity fillers, such as mineral fillers. Since the crosslinking agents utilized in the polybutadiene core compositions are expensive and/or the higher specific gravity fillers are relatively inexpensive, the addition of the polypropylene powder resin substantially lowers the cost of the golf ball cores while maintaining, or lowering, weight and compression.

[0064] The polypropylene (C₃H₅) powder suitable for use in the present invention has a specific gravity of about 0.90 g/cm³, a melt flow rate of about 4 to about 12 and a particle size distribution of greater than 99% through a 20 mesh screen. Examples of such polypropylene powder resins include those sold by the Amoco Chemical Co., Chicago, Ill., under the designations “6400 P”, “7000 P” and “7200 P”. Generally, from 0 to about 25 parts by weight polypropylene powder per each 100 parts of elastomer are included in the present invention.

[0065] Various activators may also be included in the compositions of the present invention. For example, zinc oxide and/or magnesium oxide are activators for the polybutadiene. The activator can range from about 2 to about 30 parts by weight per 100 parts by weight of the rubbers (phr) component.

[0066] Moreover, reinforcement agents may be added to the core compositions of the present invention. Since the specific gravity of polypropylene powder is very low, and when compounded, the polypropylene powder produces a lighter molded core, when polypropylene is incorporated in the core compositions, relatively large amounts of higher specific gravity fillers may be added so long as the specific core weight limitations are met. As indicated above, additional benefits may be obtained by the incorporation of relatively large amounts of higher specific gravity, inexpensive mineral fillers such as calcium carbonate. Such fillers as are incorporated into the core compositions should be in finely divided form, as for example, in a size generally less than about 30 mesh and preferably less than about 100 mesh U.S. standard size. The amount of additional filler included in the core composition is primarily dictated by weight restrictions and preferably is included in amounts of from about 10 to about 100 parts by weight per 100 parts rubber.

[0067] The preferred fillers are relatively inexpensive and heavy and serve to lower the cost of the ball and to increase the weight of the ball to closely approach the U.S.G.A. weight limit of 1.620 ounces. However, if thicker cover compositions are to be applied to the core to produce larger than normal (i.e. greater than 1.680 inches in diameter) balls, use of such fillers and modifying agents will be limited in order to meet the U.S.G.A. maximum weight limitations of 1.620 ounces. Limestone is ground calcium/magnesium carbonate and is used because it is an inexpensive, heavy filler. Ground flash filler may be incorporated and is preferably 20 mesh ground up center stock from the excess flash from compression molding. It lowers the cost and may increase the hardness of the ball.

[0068] Fatty acids or metallic salts of fatty acids may also be included in the compositions, functioning to improve moldability and processing. Generally, free fatty acids having from abut 10 to about 40 carbon atoms, and preferably having from about 15 to about 10 carbon atoms, are used. Exemplary of suitable fatty acids are stearic acid and linoleic acids, as well as mixtures thereof. An example of a suitable metallic salt of a fatty acid is zinc stearate. When included in the core compositions, the metallic salts of fatty acids are present in amounts of from about 1 to about 25, preferably in amounts from about 2 to about 15 parts by weight based on 100 parts rubber (elastomer). It is preferred that the core compositions include stearic acid as the fatty acid adjunct in an amount of from about 2 to about 5 parts by weight per 100 parts of rubber.

[0069] Diisocyanates may also be optionally included in the core compositions. When utilized, the diisocyanates are included in amounts of from about 0.2 to about 5.0 parts by weight based on 100 parts rubber. Exemplary of suitable diisocyanates is 4,4′-diphenylmethane diisocyanate and other polyfunctional isocyanates known in the art.

[0070] Furthermore, the dialkyl tin difatty acids set forth in U.S. Pat. No. 4,844,471, the dispensing agents disclosed in U.S. Pat. No. 4,838,556, and the dithiocarbamates set forth in U.S. Pat. No. 4,852,884 may also be incorporated into the polybutadiene compositions of the present invention. The specific types and amounts of such additives are set forth in the above identified patents, which are incorporated herein by reference.

[0071] The core compositions of the invention which contain polybutadiene are generally comprised of 100 parts by weight of a base elastomer (or rubber) selected from polybutadiene and mixtures of polybutadiene with other elastomers, 15 to 25 parts by weight of at least one metallic salt of an unsaturated carboxylic acid, and 0.5 to 10 parts by weight of a free radical initiator.

[0072] As indicated above, additional suitable and compatible modifying agents such as particulate polypropylene resin, fatty acids, and secondary additives such as pecan shell flour, ground flash (i.e. grindings from previously manufactured cores of substantially identical construction), barium sulfate, zinc oxide, etc. may be added to the core compositions to adjust the weight of the ball as necessary in order to have the finished molded ball (core, cover and coatings) to closely approach the U.S.G.A. weight limit of 1.620 ounces.

[0073] In producing solid golf ball cores utilizing the present compositions, the ingredients may be intimately mixed using, for example, two roll mills or an internal mixer until the composition is uniform, usually over a period of from about 5 to about 20 minutes. The sequence of addition of components is not critical. A preferred blending sequence is as follows.

[0074] The elastomer, polypropylene powder resin (if desired), fillers, zinc salt, metal oxide, fatty acid, and the metallic dithiocarbamate (if desired), surfactant (if desired), and tin difatty acid (if desired), are blended for about 7 minutes in an internal mixer such as a Banbury® (Farrel Corp.) mixer. As a result of shear during mixing, the temperature rises to about 200° F. The initiator and diisocyanate are then added and the mixing continued until the temperature reaches about 220° F. whereupon the batch is discharged onto a two roll mill, mixed for about one minute and sheeted out.

[0075] The sheet is rolled into a “pig” and then placed in a Barwell™ preformer and slugs are produced. The slugs are then subjected to compression molding at about 320° F. for about 14 minutes. After molding, the molded cores are cooled, the cooling effected at room temperature for about 4 hours or in cold water for about one hour. The molded cores can be subjected to a centerless grinding operation whereby a thin layer of the molded core is removed to produce a round core having a diameter of 1.2 to 1.5 inches. Alternatively, the cores are used in the as-molded state with no grinding needed to achieve roundness.

[0076] The mixing is desirably conducted in such a manner that the composition does not reach incipient polymerization temperatures during the blending of the various components.

[0077] Usually the curable component of the composition will be cured by heating the composition at elevated temperatures on the order of from about 275° F. to about 350° F., preferably and usually from about 290° F. to about 325° F., with molding of the composition effected simultaneously with the curing thereof. The composition can be formed into a core structure by any one of a variety of molding techniques, e.g. injection, compression, or transfer molding. When the composition is cured by heating, the time required for heating will normally be short, generally from about 10 to about 20 minutes, depending upon the particular curing agent used. Those of ordinary skill in the art relating to free radical curing agents for polymers are conversant with adjustments of cure times and temperatures required to effect optimum results with any specific free radical agent.

[0078] After molding, the core is removed from the mold and the surface thereof optionally is treated to facilitate adhesion thereof to the covering materials. Surface treatment can be effected by any of the several techniques known in the art, such as corona discharge, ozone treatment, sand blasting, and the like. Preferably, surface treatment is effected by grinding with an abrasive wheel.

[0079] In addition to using solid molded cores, wound cores may also be incorporated in the golf balls of the present invention. Such wound cores would include a generally spherical center and a rubber thread layer, or windings, enclosing the outer surface of the center.

[0080] In this regard, the generally spherical center of the wound cores may be a solid center or a liquid center. The solid center can consist of one or more layers. For example, the solid center can comprise a molded polybutadiene rubber sphere which, although smaller in size, is of similar construction to the molded cores in the two-piece molded golf balls described above.

[0081] Suitable solid centers used in the invention are not particularly limited to, but include those made of vulcanized rubber. Such solid centers may be prepared by adding to butadiene rubber, additives such as vulcanizing agents, accelerators, activating agents, fillers, modifiers and aids and then subjecting the mixture to vulcanization and molding.

[0082] The solid center (whether of single unitary construction or of multi-layers) generally is from 1 to 1.5 inches in diameter, preferably 1.0625 to 1.42 inches, with a weight of 15 grams to 36 grams, preferably 16.5 to 30 grams.

[0083] Alternatively, a liquid center can be incorporated into the wound core of the present invention. The liquid center consists of a hollow spherical bag or sack of conventional vulcanized rubber filled with a liquid, paste or gel. Examples of such a liquid include water, glycerin, sugar-water solutions, corn-syrup, saline solutions, oils, etc. and/or combinations thereof. Examples of pastes can be produced by adding clay, sodium sulfate, barytes, barium sulfate to a minor amount of ethylene glycol in water. Examples of suitable gels include hydrogels, cellulose gels, water gels, etc. The specific gravity of the liquid is, in general, 0.6 to 3 and the specific gravity of the paste is from 0.6 to 3 and the gels from 0.6 to 3. The bag or sack is, in general, from 0.05 to 0.150 inches in thickness, preferably 0.08 to 0.105 inches in thickness.

[0084] The liquid center generally is from 1 to 1.25 inches in diameter, preferably 1.0625 to 1.14 inches, with a weight of 5.5 to 25.5 grams, preferably 15 to 21 grams.

[0085] The wound core is formed by winding conventional thread rubber around the outer periphery of the solid or liquid center. The thread rubber may include, for example, those prepared by subjecting natural rubber, or a blend of natural rubber and polyisoprene rubber to vulcanization and molding. The winding process is under high tension to produce a threaded layer over the solid or liquid center. Conventional techniques may be employed in winding the thread rubber and known compositions may be used. Although the thread rubber is not limited with respect to specific gravity, dimension and gage, it usually has a specific gravity of 0.9 to 1.1, a width of 0.047 to 0.094 and a gage of 0.012 to 0.026.

[0086] The rubber thread layer has a radial thickness of 0.10 to 0.315 inches and comprises a wound core having an outer diameter of 1.52 to 1.63 inches. The overall weight of the wound core is 33 to 44 grams, preferably 35 to 39 grams.

Multi-Layer Covers

[0087] As indicated above, cover layers of the present invention golf ball preferably but not necessarily comprise an ionomer resin. High or low acid ionomers, or ionomer blends can be used, along with polyurethane, polyurea and blends thereof. The high acid ionomers which may be suitable for use in formulating the cover compositions are ionic copolymers which are the metal, i.e., sodium, zinc, magnesium, lithium, etc., salts of the reaction product of an olefin having from about 2 to 8 carbon atoms and an unsaturated monocarboxylic acid having from about 3 to 8 carbon atoms. Preferably, the ionomeric resins are copolymers of ethylene and either acrylic or methacrylic acid. In some circumstances, an additional comonomer such as an acrylate ester (i.e., iso- or n-butylacrylate, etc.) can also be included to produce a softer terpolymer. The carboxylic acid groups of the copolymer are at least partially neutralized (i.e., approximately 10% to 100%, and preferably 30% to 70%) by the metal ions. Each of the high acid ionomer resins contains greater than about 16% by weight of a carboxylic acid, and preferably from about 17% to about 25% by weight of a carboxylic acid, and more preferably from about 18.5% to about 21.5% by weight of a carboxylic acid.

[0088] The high acid ionomeric resins available from Exxon under the designation lotek®, are somewhat similar to the high acid ionomeric resins available under the Surlyn® trademark. However, since the lotek® ionomeric resins are sodium, lithium or zinc salts of poly(ethylene-acrylic acid) and the Surlyn® resins are zinc, sodium, lithium, etc. salts of poly(ethylene-methacrylic acid), distinct differences in properties exist.

[0089] Non-limiting examples of the high acid methacrylic acid based ionomers suitable for use in accordance with this invention include Surlyn® 8140(Na), 8220 (Na), 8240 (Na), 9120 (Zn), 9220 (Zn), AD8181 (Li), AD8530 (Zn), AD8531 (Na) and SEP 671 (Li). Table 1, set forth below, lists properties for two of these materials. TABLE 1 Surlyn ® Resins SURLYN ® 8140 SURLYN ® 120 (19 wt % acid) (19 wt % acid) IONOMER Cation Na Zn Melt Flow Index, g/10 min. 2.60 1.30 Specific gravity 0.96 0.97 MP, C. 88 85 FP, C. 49 50 MECHANICAL PROPERTIES Tensile Strength, kpsi (MPa) 5.0 (34.5) 3.8 (26.2) Yield Strength, kpsi (MPa) 2.8 (19.3) 2.4 (16.6) Elongation, % 340 280 Flex Mod, kpsi (MPa) 71 (490) 84 (440) Shore D Hardness 70 69

[0090] Examples of the high acid acrylic acid based ionomers suitable for use in the present invention also include lotek® high acid ethylene acrylic acid ionomers produced by Exxon such as 1001, 1002, 959, 960, 989, 990, 1003, 1004, 993, and 994. In this regard, lotek® 959 is a sodium ion neutralized ethylene-acrylic acid copolymer. According to Exxon, lotek® 959 and 960 contain from about 19.0 to about 21.0% by weight acrylic acid with approximately 30 to about 70 percent of the acid groups neutralized with sodium and zinc ions, respectively. The physical properties of these and other high acid acrylic acid based ionomers are set forth in Table 2 as follows: TABLE 2 Iotek ® Resins PROPERTY 1001 1002 959 1003 1004 960 Melt index, 1.00 1.60 2.00 1.10 2.00 1.80 g/10 min. Cation Na Na Na Zn Zn Zn Melting 183.0 183.0 172.0 180.0 180.5 174.0 point, F. Crystalliza- 107.0 110.0 106.0 125.0 126.5 120.0 tion point, F. Vicat 125.0 125.0 130.0 133.0 131.0 131.0 Softening Point, F. Tensile @@ 34.4 31.7 4600 24.8 20.6 3500 Break MPa MPa psi MPa MPa psi Tensile @@ 21.8 22.5 — 14.9 14.0 — Yield MPa MPa MPa MPa 1% Secant 356 418 350 145 128 140 Modulus MPa MPa MPa MPa MPa MPa Elongation 341 348 325 387 437 430 @@ Break, % Hardness, 63 62 66 54 53 57 Shore D Flexural 365 380 66,000 147 130 27,000 Modulus MPa MPa psi MPa MPa psi Density .9558 .9557 .968 .9715 .9691 .980 g/cm³ g/cm³ g/cm³ g/cm³ g/cm³ g/cm³ EX 989 EX 993 EX 994 EX 990 Melt index g/10 min 1.30 1.25 1.32 1.24 Moisture ppm 482 214 997 654 Cation Type — Na Li K Zn M+ content wt % 2.74 0.87 4.54 0.00 by AAS Zn content wt % 0.00 0.00 0.00 3.16 by AAS Density kg/m3 959 945 976 977 Vicat soften- C. 52.5 51.0 50.0 55.0 ing point Crystalliza- C. 40.1 39.8 44.9 54.4 tion point Melting C. 82.6 81.0 80.4 81.0 point Tensile at MPa 23.8 24.6 22.0 16.5 yield Tensile at MPa 32.3 31.1 29.7 23.8 break Elongation at % 330 260 340 357 break 1% secant MPa 389 379 312 205 modulus Flexural MPa 340 368 303 183 modulus Abrasion mg 20.0 9.2 15.2 20.5 resistance Hardness — 62 62.5 61 56 Shore D Zwick % 61 63 59 48 rebound

[0091] Furthermore, as a result of the development by the assignee of this application of a number of new ionomers neutralized to various extents by several different types of metal cations, such as by manganese, lithium, potassium, calcium and nickel cations, several new ionomers and/or ionomer blends besides sodium, zinc and magnesium high acid ionomers or ionomer blends are now available for golf ball cover production. In particular it has been found that new cation neutralized high acid ionomer blends produce inner cover layer compositions exhibiting enhanced hardness and resilience due to synergies which occur during processing. Consequently, the metal cation neutralized high acid ionomer resins recently produced can be blended to produce substantially higher C.O.R.'s than those produced by the low acid ionomer inner cover compositions presently commercially available.

[0092] More particularly, several new metal cation neutralized high acid ionomer resins have been produced by the inventor by neutralizing, to various extents, high acid copolymers of an alpha-olefin and an alpha, beta-unsaturated carboxylic acid with a wide variety of different metal cation salts. It has been found that numerous new metal cation neutralized high acid ionomer resins can be obtained by reacting a high acid copolymer (i.e. a copolymer containing greater than 16% by weight acid, preferably from about 17 to about 25 weight percent acid, and more preferably about 20 weight percent acid), with a metal cation salt capable of ionizing or neutralizing the copolymer to the extent desired (i.e. from about 10% to 90%).

[0093] The base copolymer is made up of greater than 16% by weight of an alpha, beta-unsaturated carboxylic acid and an alpha-olefin. As indicated above, a softening comonomer can be included in the copolymer. Generally, the alpha-olefin has from 2 to 10 carbon atoms and is preferably ethylene, and the unsaturated carboxylic acid is a carboxylic acid having from about 3 to 8 carbons. Examples of such acids include acrylic acid, methacrylic acid, ethacrylic acid, chloroacrylic acid, crotonic acid, maleic acid, fumaric acid, and itaconic acid, with acrylic acid being preferred.

[0094] The softening comonomer that can be optionally included in the inner cover layer for the golf ball of the invention may be selected from the group consisting of vinyl esters of aliphatic carboxylic acids wherein the acids have 2 to 10 carbon atoms, vinyl ethers wherein the alkyl groups contains 1 to 10 carbon atoms, and alkyl acrylates or methacrylates wherein the alkyl group contains 1 to 10 carbon atoms. Suitable softening comonomers include vinyl acetate, methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, butyl acrylate, butyl methacrylate, or the like.

[0095] Consequently, examples of a number of copolymers suitable for use to produce the high acid ionomers included in the present invention include, but are not limited to, high acid embodiments of an ethylene/acrylic acid copolymer, an ethylene/methacrylic acid copolymer, an ethylene/itaconic acid copolymer, an ethylene/maleic acid copolymer, an ethylene/methacrylic acid/vinyl acetate copolymer, an ethylene/acrylic acid/vinyl alcohol copolymer, etc. The base copolymer broadly contains greater than 16% by weight unsaturated carboxylic acid, from about 39 to about 83% by weight ethylene and from 0 to about 40% by weight of a softening comonomer. Preferably, the copolymer contains about 20% by weight unsaturated carboxylic acid and about 80% by weight ethylene. Most preferably, the copolymer contains about 20% acrylic acid with the remainder being ethylene.

[0096] Along these lines, examples of the preferred high acid base copolymers which fulfill the criteria set forth above, are a series of ethylene-acrylic copolymers which are commercially available from Dow Chemical Company, Midland, Michigan, under the Primacor® designation. These high acid base copolymers exhibit the typical properties set forth below in Table 3. TABLE 3 Typical Properties of Primacor ® Ethylene-Acrylic Acid Copolymers MELT INDEX, g/10 TENSILE FLEXURAL VICAT DENSITY, min YD. ST MODULUS SOFT PT SHORE D GRADE PERCENT g/cc D-1238, (psi) (psi) (C.) HARDNESS ASTM ACID D-792 190 C. D-638 D-790 D-1525 D-2240 5980 20 0.96  300 — 4800 43 50 5990 20 0.96 1300 650 2600 40 42 5981 20 0.96  300 900 3200 46 48 5983 20 0.96  500 850 3100 44 45 5991 20 0.95 2600 635 2600 38 40

[0097] Due to the high molecular weight of the Primacor® 5981 grade of the ethylene-acrylic acid copolymer, this copolymer is the more preferred grade utilized in the invention.

[0098] The metal cation salts utilized in the present invention are those salts which provide the metal cations capable of neutralizing, to various extents, the carboxylic acid groups of the high acid copolymer. These include acetate, oxide or hydroxide salts of lithium, calcium, zinc, sodium, potassium, nickel, magnesium, and manganese.

[0099] Examples of such lithium ion sources are lithium hydroxide monohydrate, lithium hydroxide, lithium oxide and lithium acetate. Sources for the calcium ion include calcium hydroxide, calcium acetate and calcium oxide. Suitable zinc ion sources are zinc acetate dihydrate and zinc acetate, a blend of zinc oxide and acetic acid. Examples of sodium ion sources are sodium hydroxide and sodium acetate. Sources for the potassium ion include potassium hydroxide and potassium acetate. Suitable nickel ion sources are nickel acetate, nickel oxide and nickel hydroxide. Sources of magnesium include magnesium oxide, magnesium hydroxide, and magnesium acetate. Sources of manganese include manganese acetate and manganese oxide.

[0100] The new metal cation neutralized high acid ionomer resins are produced by reacting the high acid base copolymer with various amounts of the metal cation salts above the crystalline melting point of the copolymer, such as at a temperature from about 200° F. to about 500° F., preferably from about 250° F. to about 350° F. under high shear conditions at a pressure of from about 10 psi to 10,000 psi. Other blending techniques may also be used. The amount of metal cation salt utilized to produce the new metal cation neutralized high acid based ionomer resins is the quantity which provides a sufficient amount of the metal cations to neutralize the desired percentage of the carboxylic acid groups in the high acid copolymer. The extent of neutralization is generally from about 10% to about 90%.

[0101] When the acid groups of copolymers of acrylic acid and ethylene sold by Dow Chemical Co. (Midland, Mich.) and designated as Primacor® 5981 were neutralized to various weight percentages using a number of different cations, a number of different high acid ionomer resins were produced. Due to differences in the nature of the cation salts, the amount of cation salts utilized, etc., the new high acid ionomer resins produced differed substantially in the extent of neutralization and in melt indices, as well as in resilience (i.e. C.O.R.) and hardness values.

[0102] For the purpose of determining the weight percent of neutralization of the carboxylic acid groups in the acrylic acid/ethylene copolymer after reacting with various cation salts, it was assumed that one mole of sodium (Na⁺), potassium (K⁺), and lithium (Li⁺) neutralized one mole of acrylic acid, and that one mole of zinc (Zn²⁺), magnesium (Mg²⁺), manganese (Mn²⁺), calcium (Ca²⁺) and nickel (Ni²⁺) neutralized two moles of acrylic acid. The calculations of neutralization were based upon an acrylic acid molecular weight of 79 g/m, giving 0.2778 moles per 100 grams of copolymer.

[0103] As indicated below in Table 4, the various cation salts were added in variable amounts to the 20 weight percent acrylic acid/ethylene copolymer in order to determine the optimal level of neutralization for each of the cations. In Table 4, NaOH refers to sodium hydroxide (formula weight of 40). MnAc refers to manganese acetate tetrahydrate having a formula weight of 245. LiOH is lithium hydroxide, fwt=24. KOH is potassium hydroxide, fwt=56. ZnAc is zinc acetate dihydrate, fwt=219.5. MgAc is magnesium acetate tetrahydrate, fwt=214.4. CaAc is calcium acetate, fwt=158. MgO is magnesium oxide, fwt=40.3. NiAc is nickel acetate, fwt=176.8. All of these cation salts are solids at room temperature.

[0104] The specific cation salts were added in differing amounts with the 20 weight percent acrylic acid/ethylene copolymer (i.e. the Primacor® 5981) to an internal mixer (Banbury® type) for the neutralization reaction. The only exception was calcium acetate, which, due to problems encountered in solid form, was added as a 30 wt % solution in water.

[0105] In the neutralization reaction, the cation salts solubilized in the Primacor® 5981 acrylic acid/ethylene copolymer above the melting point of the copolymer and a vigorous reaction took place with a great deal of foaming occurring as the cation reacted with the carboxylic acid groups of the acrylic acid/ethylene copolymer and the volatile by-products of water (in the case of oxides or hydroxides) or acetic acid (when acetates are used) were evaporated. The reaction was continued until foaming ceased (i.e. about 30-45 minutes at 250 to 350° F.), and the batch was removed from the Banbury® mixer. Mixing continued of the batch obtained from the mixer on a hot two-roll mill (175 to 250° F.) to complete the neutralization reaction. The extent of the reaction was monitored by measuring melt flow index according to ASTM D-1238-E. As indicated below, the neutralized products exhibited different properties depending upon the nature and amount of the cation salts utilized. TABLE 4 Wt % Wt % Formulation Cation Neutral- Melt Shore D No. Salt ization Index C.O.R. Hardness  1(NaOH) 6.98 67.50 0.90 0.80 71  2(NaOH) 5.66 54.00 2.40 0.81 73  3(NaOH) 3.84 35.90 12.20  0.81 69  4(NaOH) 2.91 27.00 17.50  0.81 (brittle)  5(MnAc) 19.60  71.70 7.50 0.81 73  6(MnAc) 23.10  88.30 3.50 0.81 77  7(MnAc) 15.30  53.00 7.50 0.81 72  8(MnAc) 26.50  106.00  0.70 0.81 (brittle)  9(LiOH) 4.54 71.30 0.60 0.81 74 10(LiOH) 3.38 52.50 4.20 0.82 72 11(LiOH) 2.34 35.90 18.60  0.81 72 12(KOH) 5.30 36.00 19.30  Broke 70 13(KOH) 8.26 57.90 7.18 0.80 70 14(KOH) 10.70  77.00 4.30 0.80 67 15(ZnAc) 17.90  71.50 0.20 0.81 71 16(ZnAc) 13.90  53.00 0.90 0.80 69 17(ZnAc) 9.91 36.10 3.40 0.79 67 18(MgAc) 17.40  70.70 2.80 0.81 74 19(MgAc) 20.60  87.10 1.50 0.81 76 20(MgAc) 13.80  53.80 4.10 0.81 74 21(CaAc) 13.20  69.20 1.10 0.81 74 22(CaAc) 7.12 34.90 10.10  0.81 70 Controls: 50/50 Blend of Ioteks ® 8000/7030 C.O.R. = .810/65 Shore D Hardness DuPont High Acid Surlyn ® 8422 (Na) C.O.R. = .811/70 Shore D Hardness DuPont High Acid Surlyn ® 8162 (Zn) C.O.R. = .807/65 Shore D Hardness Exxon High Acid Iotek ® EX-960 (Zn) C.O.R. = .796/65 Shore D Hardness Wt % Formulation Cation Wt % Melt No. Salt Neutralization Index C.O.R. 23(MgO) 2.91 53.50 2.50 0.81 24(MgO) 3.85 71.50 2.80 0.81 25(MgO) 4.76 89.30 1.10 0.81 26(MgO) 1.96 35.70 7.50 0.81 Control for Formulations 23-26 is 50/50 Iotek 8000/7030, C.O.R. = .814 Formulation 26 C.O.R. was normalized to that control accordingly. Wt % Formulation Cation Wt % Melt Shore D No. Salt Neutralization Index C.O.R. Hardness 27(NiAc) 13.04  61.10 0.20 0.80 71 28(NiAc) 10.71  48.90 0.50 0.80 72 29(NiAc) 8.26 36.70 1.80 0.80 69 30(NiAc) 5.66 24.40 7.50 0.79 64 Control for formulation No. 27-30 is 50/50 Iotek 8000/7030, C.O.R. = .807

[0106] When compared to low acid versions of similar cation neutralized ionomer resins, the new metal cation neutralized high acid ionomer resins exhibit enhanced hardness, modulus and resilience characteristics. These are properties that are particularly desirable in a number of thermoplastic fields, including the field of golf ball manufacturing.

[0107] As will be further noted in the examples below, either or both high and low acid ionomer resins may be used in the cover compositions so long as the molded cover layers have a Shore D hardness of 60 or more, and more preferably 55 or more.

[0108] For example, one or more low acid (i.e. 16 weight % and/or less) hard ionomers may be included in the present invention. The hard (high modulus) ionomers suitable for use in the present invention include those ionomers having a hardness greater than 50 on the Shore D scale as measured in accordance with ASTM method D-2240, and a flexural modulus from about 15,000 to about 70,000 psi as measured in accordance with ASTM method D-790.

[0109] The hard ionomer resins utilized to produce the cover compositions are ionic copolymers which are the sodium, zinc, magnesium or lithium salts of the reaction product of an olefin having from 2 to 8 carbon atoms and an unsaturated monocarboxylic acid having from 3 to 8 carbon atoms. The carboxylic acid groups of the copolymer may be totally or partially (i.e. approximately 15-75 percent) neutralized.

[0110] Preferably, the hard ionomeric resins are copolymers of ethylene and either acrylic and/or methacrylic acid, with copolymers of ethylene and acrylic acid the most preferred. In addition, two or more types of hard ionomeric resins may be blended into the cover compositions in order to produce the desired properties of the resulting golf balls.

[0111] Examples of commercially available hard ionomeric resins which may be utilized in the present invention include the hard sodium ionic copolymer sold under the trademark Surlyn® 8940 and the hard zinc ionic copolymer sold under the trademark Surlyn® 9910. Surlyn® 8940 is a copolymer of ethylene with methacrylic acid with about 15 weight percent acid which is about 29% neutralized with sodium ions. This resin has an average melt flow index of about 2.8. Surlyn® 9910 is a copolymer of ethylene and methacrylic acid with about 15 weight percent acid which is about 58% neutralized with zinc ions. The average melt flow index of Surlyn® 9910 is about 0.7. The typical properties of Surlyn® 9910 and 8940 are set forth below. TABLE 5 Typical Properties of Commercially Available Hard Surlyn ® Resins Suitable for Use in the Present Invention ASTM D 8940 9910 8920 8528 9970 9730 Cation Type Sodi- Zinc Sodi- Sodi- Zinc Zinc um um um Melt flow index, D01238 2.8 0.7 0.9 1.3 14.0 1.6 gms/10 min. Specific Gravity, D-792 0.95 0.97 0.95 0.94 0.95 0.95 g/cm³ Hardness, Shore D-2240 66 64 66 60 62 63 D Tensile Strength, D-638 (4.8) (3.6) (5.4) (4.2) (3.2) (4.1) (kpsi), MPa 33.1 24.8 37.2 29.0 22.0 28.0 Elongation, % D-638 470 290 350 450 460 460 Flexural D-790 (51) (48) (55) (32) (28) (30) Modulus, (kpsi) 350 330 380 220 190 210 MPa Tensile Impact D-18225 1020 1020 865 1160 760 1240 (23° C.) (485) (485) (410) (550) (360) (590) KJ/m₂ (ft.-lbs./ in²) Vicat Tempera- D-1525 63 62 58 73 61 73 ture, ° C.

[0112] In addition, examples of the more pertinent acrylic acid based hard ionomer resins suitable for use in the present invention sold under the lotek® trademark by the Exxon Corporation include lotek® 4000 (formerly Escor® 4000), lotek® 4010, lotek® 8000 (formerly Escor® 900), lotek® 8020, and lotek® 8030. The typical properties of the lotek® hard ionomers are set forth below in Table 6. TABLE 6 Typical Properties of Iotek ® Ionomers ASTM Method Units 4000 4010 8000 8020 8030 Resin Properties Cation Type zinc zinc sodium sodium sodium Melt Index D-1238 g/10 2.50 1.50 0.80 1.60 2.80 min. Density D-1505 kg/m³ 963.00 963.00 954.00 960.00 960.00 Melting Point D-3417 C. 90.0 90.0 90.0 87.5 87.5 Crystallization Point D-3417 C. 62 64 56 53 55 Vicat Softening Point D-1525 C. 62 63 61 64 67 % Wt Acrylic Acid 16 11 % of Acid Groups 30 40 cation neutralized Plaque Properties (3 mm thick, compression molded) Tensile at break D-638 MPa 24.0 26.0 36.0 31.5 28.0 Yield point D-638 MPa none none 21.0 21.0 23.0 Elongation at break D-638 % 395 420 350 410 395 1% Secant modulus D-638 MPa 160 160 300 350 390 Shore Hardness D D-2240 — 55 55 61 58 59 Film Properties (50 micron film 2.2:1 Blow-up ratio) Tensile at Break MD D-882  MPa 41 39 42 52 47.4 TD D-882  MPa 37 38 38 38 40.5 Yield Point MD D-882  MPa 15 17 17 23 21.6 TD D-882  MPa 14 15 15 21 20.7 Elongation at Break MD D-882  % 310 270 260 295 305 TD D-882  % 360 340 280 340 345 1% Secant modulus MD D-882  MPa 210 215 390 380 380 TD D-882  MPa 200 225 380 350 345 Dart Drop Impact D-1709 g/ 12.40 12.50 20.30 micron ASTM Method Units 7010 7020 7030 Resin Properties Cation type zinc zinc zinc Melt Index D-1238 g/10 min. 0.80 1.50 2.50 Density D-1505 kg/m³ 960 960 960 Melting Point D-3417 C. 90 90 90 Crystallization Point D-3417 C. — — — Vicat Softening Point D-1525 C. 60 63 62.5 % Wt Acrylic Acid — — — % of Acid Groups — — — cation neutralized Plaque Properties (3 mm thick, compression molded) Tensile at break D-638  MPa 38 38 38 Yield Point D-638  MPa none none none Elongation at break D-638  % 500 420 395 1% Secant modulus D-638  MPa — — — Shore Hardness D D-2240 — 57 55 55

[0113] In addition to the above, non-ionomeric materials can also be blended with the ionomers, or used separately, to produce the cover layer of the invention. Non-limiting examples of materials that can be utilized include ethylene-ethyl acrylate, ethylene-methyl acrylate, ethylene-vinyl acetate, low density polyethylene, linear low density polyethylene, metallocene catalyzed polyolefins such as Engage® polyolefins available from Dow Chemical and Exact® polyolefins available from Exxon, non-ionomeric acid copolymers such as Primacor®, available from Dow Chemical, and Nucrel®, available from DuPont, and a variety of thermoplastic elastomers, including Kraton®, available from Shell, Santoprene®, available from Monsanto, and Hytrel®, available from DuPont, etc. Furthermore functionalized EPDM, such as maleated EPDM, nylon, and nylon-ionomer graft copolymers.

[0114] A wide array of nylon-containing or nylon-based materials may be incorporated into the various cover layers of the present invention golf ball. Preferred nylon materials for utilizing in the present invention golf ball are described in U.S. Pat. No. 5,886,103 herein incorporated by reference.

[0115] Moreover, a wide array of polyurethane materials can be utilized in one or more cover layers of the present invention golf balls. Before turning attention to the specifics of such materials, it is instructive to review the features and terminology associated with polyurethanes.

[0116] Polyurethanes are polymers which are used to form a broad range of products. They are generally formed by mixing two primary ingredients during processing. For the most commonly used polyurethanes, the two primary ingredients are a polyisocyanate (for example, diphenylmethane diisocyanate monomer (“MDI”) and toluene diisocyanate (“TDI”) and their derivatives) and a polyol (for example, a polyester polyol or a polyether polyol).

[0117] A wide range of combinations of polyisocyanates and polyols, as well as other ingredients, are available. Furthermore, the end-use properties of polyurethanes can be controlled by the type of polyurethane utilized, i.e., whether the material is thermoset (cross linked molecular structure) or thermoplastic (linear molecular structure).

[0118] Crosslinking occurs between the isocyanate groups (—NCO) and the polyol's hydroxyl end-groups (—OH). Additionally, the end-use characteristics of polyurethanes can also be controlled by different types of reactive chemicals and processing parameters. For example, catalysts are utilized to control polymerization rates. Depending upon the processing method, reaction rates can be very quick (as in the case for some reaction injection molding systems (i.e., “RIM”)) or may be on the order of several hours or longer (as in several coating systems). Consequently, a great variety of polyurethanes are suitable for different end-users.

[0119] Polyurethane has been used for golf balls and other game balls as a cover material. Polyurethanes are typically classified as thermosetting or thermoplastic. Commercially available polyurethane golf balls have been made of thermoset polyurethanes. A polyurethane becomes irreversibly “set” when a polyurethane prepolymer is crosslinked with a polyfunctional curing agent, such as polyamine and polyol. The prepolymer typically is made from polyether or polyester. Diisocyanate polyethers are preferred because of their water resistance.

[0120] The physical properties of thermoset polyurethanes are controlled substantially by the degree of crosslinking. Tightly crosslinked polyurethanes are fairly rigid and strong. A lower amount of crosslinking results in materials that are flexible and resilient. Thermoplastic polyurethanes have some crosslinking, but purely by physical means. The crosslinking bonds can be reversibly broken by increasing temperature, as occurs during molding or extrusion. In this regard, thermoplastic polyurethanes can be injection molded, and extruded as sheet and blown film. They can be used to up to about 350° F. and are available in a wide range of hardnesses.

[0121] U.S. Pat. No. 5,006,297 indicates that while thermoplastic and thermosetting polyurethanes are known, thermosets have been found to produce better cover stocks for golf balls. Additionally, while thermoplastic polyurethanes can be used to form game balls, they lack the scuff and cut resistance of a crosslinked polyurethane. Similarly, thermoplastic polyurethanes do not readily crosslink.

[0122] Polyurethanes typically are formed by reacting a polyol with a polyisocyanate. In some cases, the polyisocyanate is in the form of a polyurethane prepolymer formed from a polyether or polyester and a polyisocyanate. The polyol or polyamine is typically referred to as a “curing” agent. Examples of reactants used to form polyurethanes by this technique are discussed in U.S. Pat. No. 5,006,297, herein incorporated by reference. In other cases a polyester or acrylic polyol is reacted with a polyisocyanate.

[0123] Two types of polyisocyanates are predominantly used to make polyurethanes, diphenylmethane diisocyanate monomer (MDI) and its derivatives, and toluene diisocyanate (TDI) and its derivatives.

[0124] MDI is the most widely used polyisocyanate. Both rigid and flexible foams, reaction injection moldings, elastomers, coatings, and casting compounds are made from MDI. There are three basic grades of MDI: polymeric MDI, pure MDI, and pure MDI derivatives.

[0125] Polymeric MDI is used in both cellular and non-cellular products. However, because of the high thermal insulation properties possible with polymeric MDI, its main use is in closed-cell, rigid foam insulation for the construction and refrigeration industries. Other uses are high-resilience (HR) flexible foam, carpet backing, and binders.

[0126] Pure MDI, which is produced from polymeric MDI, is a low-melting-temperature (about 100° F.) solid. Its primary use is in thermoplastic and cast elastomers. It also is used as an additive for synthetic fibers to achieve high fiber tenacity and elongation.

[0127] Pure MDI derivatives are tailored to provide specific processing and reaction characteristics. A major use for these solvent-free liquids is in reaction injection molding (RIM), but they also find application in integral skin moldings, semi-flexible moldings, and cast elastomers.

[0128] Toluene diisocyanate, TDI, is used almost exclusively to make flexible foam. TDI, however, also finds some use in elastomers, sealants, and coatings. TDI's generally are water-white liquids which have much higher isocyanate (—NCO) contents than any MDI, but lower molecular weights.

[0129] MDI and TDI also are blended, particularly for producing flexible molded foams. The free-flowing, brown liquid blends have nearly as high isocyanate contents as TDI.

[0130] Urethanes obtained from aromatic diisocyanates undergo slow oxidation in the presence of air and light, causing discoloration, which is unacceptable in some applications. Polyurethanes obtained from aliphatic diisocyanates are color-stable, although it is necessary to add antioxidants and uv-stabilizers to the formulation to maintain the physical properties with time. The least costly aliphatic diisocyanate is hexamethylene diisocyanate (HDI), which is obtained by phosgenating the nylon intermediate hexamethylenediamine. Because of its low boiling point, HDI is mostly used in form of its derivatives, such as biurets, allophanates, dimers, or trimers. It is contemplated that isophorone diisocyanate (IPDI) and its derivatives; and hydrogenated MDI (HMDI) and cyclohexame diisocyanate (CHDI) may be used in the formulations described herein.

[0131] A wide array of isocyanates may be used in forming polyurethanes for use in the present invention, such as p-phenylene diisocyanate (PPDI) (CAS Registry No. 104-49-4); toluene diisocyanate (TDI) (CAS Registry No. 1321-38-6); 4,4′-methylenebis-(phenylisocyanate) (MDI) (CAS Registry No. 101-68-8); polymethylene polyphenyl isocyanate (PMDI) (CAS Registry No. 9016-87-9); 1,5-naphthalene diisocyanate (NDI) (CAS Registry No. 3173-72-6); bitolylene diisocyanate (TODI) (CAS Registry No. 91-97-4); m-xylylene diisocyanate (XDI) (CAS Registry No. 3634-83-1); m-tetramethyl-xylylene (TMXDI) (CAS Registry No. 58067-42-8); hexamethylene diisocyanate (HDI) (CAS Registry No. 822-06-0); 1,6-diisocyanato-2,2,4,4-tetra-methylhexane (TMDI) (CAS Registry No. 83748-30-5); 1,6-diisocyanato-2,4,4-trimethylhexane (TMDI) (CAS Registry No. 15646-96-5); trans-cyclohexane-1,4-diisocyanate (CHDI) (CAS Registry No. 2556-36-7); 1,3-bis(isocyanato-methyl)cyclohexane (HXDI) (CAS Registry No. 38661-72-2); 3-isocyanato-methyl-3,5,5-trimethylcyclo-hexyl isocyanate (IPDI) (CAS Registry No. 4098-171-9); dicyclohexylmethane diisocyanate (HMDI) (CAS Registry No. 5124-30-1).

[0132] Two basic types of polyols are used in polyurethanes systems: polyesters and polyethers. Polyethers are the most widely used.

[0133] Often in referring to polyols, their functionality is specified. The functionality pertains to the number of reactive sites, which in turn, controls crosslinking. The more crosslinked (higher functionality), the more rigid will be the polyurethane. Functionality is controlled by the initiator used to manufacture the polyol. Glycerine, for example, is commonly used to initiate triol (3 functional) polyols. To this initiator is added an oxide such as propylene oxide, ethylene oxide, or a combination, to extend the molecular chain and tailor final processing and performance characteristics of the polyol. Triols typically are used to produce flexible foams; diols are used for elastomers, coatings, and sealants; and tetrols typically are used for rigid foams.

[0134] Polyether-based polyols have greater resistance to hydrolysis. Polyether polyols can be modified by the in-situ polymerization of acrylonitrile/styrene monomers. The resulting graft polyols generally produce flexible foams with improved load-bearing properties as well as greater tensile and tear strengths. Depending on the backbone on which these vinyl monomers are grafted, a wide range of performance characteristics can be developed.

[0135] Polyether polyols are high molecular weight polymers that range from viscous liquids to waxy solids, depending on structure and molecular weight. Most commercial polyether polyols are based on the less expensive ethylene or propylene oxide or on a combination of the two. Block copolymers are manufactured first by the reaction of propylene glycol with propylene oxide to form a homopolymer. This polymer upon further reaction with ethylene oxide to form the block copolymer. Because primary hydroxyl groups, resulting from the polymerization of the ethylene oxide, are more reactive than secondary hydroxyl groups, the polyols produced in this manner are more reactive. Random copolymers are obtained by polymerizing mixtures of propylene oxide and ethylene oxide. The viscosity of polyether polyols increases with hydroxyl equivalent weight. The higher molecular weight polyether polyols are soluble in organic solvents. Poly(propylene oxide) is soluble in water up to a molecular weight of 760, and copolymerization with ethylene oxide expands the range of water solubility.

[0136] Polyester polyols yield polyurethanes with greater strength properties, wear resistance, and thermal stability than polyether polyurethanes, and they can absorb more energy. These materials, however, are generally more expensive than polyethers.

[0137] Polyester polyols are based on saturated aliphatic or aromatic carboxylic acids and diols or mixtures of diols. The carboxylic acid of choice is adipic acid because of its favorable cost/performance ratio. For elastomers, linear polyester polyols of about 2000 mol wt are preferred. Branched polyester polyols, formulated from higher functional glycols, are used for foam and coatings applications. Phthalates and terephthalates are also used.

[0138] Polyester polyols are typically classed by molecular weight. Low molecular weight polyols (less than 1500) are used in coatings, casting compounds, and rigid foams. Medium molecular weight polyols (1550 to 2500) are used in elastomers. And, high molecular weight polyols (greater than 2500) are used in flexible foams.

[0139] Thermoset polyurethanes are typically crosslinked and cannot be repeatedly thermoformed. On the other hand, thermoplastic polyurethanes are similar to other thermoplastics in that they can be repeatedly plasticized by the influence of temperature and pressure.

[0140] The crosslinkable thermoplastic polyurethane used to form a game ball according to the present invention is initially a thermoplastic, and in this state can be melted and solidified repeatedly. However, the material can be readily crosslinked, thereby increasing its hardness and providing that it cannot be reversibly melted without thermal degradation.

[0141] The melt viscosity of a thermoplastic polyurethane (TPU) depends on the weight-average molecular weight and is influenced by chain length and branching. TPUs are viscoelastic materials, which behave like a glassy, brittle solid, an elastic rubber, or a viscous liquid, depending on temperature and time scale of measurement. With increasing temperature, the material becomes rubbery because of the onset of molecular motion. At higher temperatures a free-flowing liquid forms.

[0142] The melt temperature of a polyurethane is important for processibility. Melting should occur well below the decomposition temperature. Below the glass-transition temperature (T_(g)), the molecular motion is frozen, and the material is only able to undergo small-scale elastic deformations. For amorphous polyurethane elastomers, the T_(g) of the soft segment is about −50 to −60° C., whereas for the amorphous hard segment, T_(g) is in the 20-100° C. range.

[0143] The choice of macrodiol influences the low temperature performance, whereas the modulus, i.e. hardness, stiffness, and load-bearing properties, increases with increasing hard-segment content.

[0144] A wide array of crosslinkable thermoplastic polyurethanes can be used in the present invention. For example, EBXL-TPU is a thermoplastic polyurethane recently made available from Zylon Polymers, 23 Mountain Avenue, Monsey, N.Y. 10952. EBXL-TPU is a pelletized, medical grade, polyether or polyester based thermoplastic polyurethane, reactor modified to allow crosslinking by ionizing radiation. It is a low melt index material suitable for extrusion into profiles, film and sheet, or injection molding. Once crosslinked, the material combines the ease of processing and toughness of TPU with the improved resistance to water, solvents and elevated temperatures characteristic of thermoset materials. Table 7 below, sets forth details of this preferred material. TABLE 7 EBXL-TPU Typical Physical Properties PROPERTY VALUE UNITS Radiation 12.5-15 MegaRads Shore Hardness 80 Shore A Specific Gravity 1.04 gr/cc Tensile Strength 5000 psi Ultimate Elongation 425 % Compression set, 50 % 70 hrs @ 100 deg C. Melt Flow Index 2 gms/10 min FLUID RESISTANCES Water, no effect 24 hrs @ 23 C. Isopropyl Alcohol, no effect 100% 24 hrs @ 23 C. Tetrahydrofuran, swells, does not dissolve 24 hrs @ 23 C.

[0145] A further preferred class of crosslinkable thermoplastic polyurethanes is a commercially available polyurethane from BASF, designated as Elastollan®. Properties of several specific formulations of Elastollan® polyurethanes are set forth in Table 8 below. TABLE 8 Physical ASTM properties¹ Units Method 1175AW³ 1180A 1185A 1190A 1195A 1154D 1160D 1164D 1174D Specific gravity gr/cc D-792 1.14 1.11 1.12 1.13 1.14 1.16 1.17 1.18 1.19 Hardness Shore D-224 A 76 ± 2 80 ± 2 86 ± 2 91 ± 2 95 ± 2 — — — — D — — — 42 ± 2 47 ± 2 53 ± 2 60 ± 2 64 ± 2 73 ± 2 Tensile strength MPa D-412 30 32 33 37 36 40 40 41 45 psi 4500 4700 4800 5300 5200 5800 5800 6000 6500 Tensile stress D-412 @ 100% elongation MPa 4.3 5.5 7.6 10 12 20 22 25 32 psi 620 800 1100 1500 1750 2900 3200 3600 4600 @ 300% elongation MPa 8.3 10 12 17 21 30 33 33 38 psi 1180 1500 1750 2500 3000 4300 4800 4800 5500 Elongation @ brk. % D-412 740 600 640 575 490 460 415 425 350 Tensile set @ brk. % D-412 — 45 70 75 65 70 60 90 80 Tear strength kN/m D-624 80 90 105 125 140 180 205 220 255 pli DIE C 460 515 600 715 800 1025 1170 1250 1450 Abrasion resistance mg D-1044² 25 30 45 55 75 50 55 75 (loss) (Taber)

[0146] Elastollan® 1100 series of products are polyether-based thermoplastic polyurethanes. They exhibit excellent low temperature properties, hydrolysis resistance and fungus resistance. These products can be injection and blow molded and extruded.

[0147] BASF indicates that Elastollan® 1175AW, 80A, 90A and 95A are suitable for extrusion. And, Elastollan® 1175AW to 1174D are suitable for injection molding. BASF further provides that a grade should be dried before processing. Elastollan® can be stored for up to 1 year in its original sealed container. Containers should be stored in a cool, dry area. Elastollan® TPU's from BASF are commercial TPU's but will not crosslink using irradiation unless a particular reactive co-agent such as Liquiflex™ H, described below, is added. Nearly any other commercially available TPU such as Urepan®, Pellethane®, Morthane®, Desmopan®, etc. can be used provided it is compounded with a co-agent that readily crosslinks with radiation.

[0148] Liquiflex™ is a commercially available hydroxyl terminated polybutadiene (HTPB), from Petroflex. It is believed that this co-agent enables the thermoplastic polyurethane to crosslink upon exposure to radiation. It is believed that the previously noted thermoplastic polyurethane EBXL-TPU from Zylon contains a co-agent similar to Liquiflex™.

[0149] In accordance with the present invention, it is most preferred that at least one of the cover layers of a multi-layer assembly comprise a polyurethane. More preferably, the one or more cover layers comprise a majority proportion, by weight, of a polyurethane.

[0150] As indicated above, numerous ways are known to induce crosslinking in a polymer by free radical initiation, including peroxide initiation and irradiation. The golf ball covers of the present invention preferably are crosslinked by irradiation, and more preferably light rays such as gamma or UV irradiation. Furthermore, other forms of particle irradiation, including electron beam also can be used. Gamma radiation is preferred as golf balls or game balls can be irradiated in bulk. Gamma penetrates very deep but also increases crosslinking of the inner core and the compression of the core has to be adjusted to allow for the increase in hardness.

[0151] Electron beam techniques are faster but cannot be used for treating in bulk as the electron beam does not penetrate very deep and the product needs to be rotated to obtain an even crosslink density.

[0152] The type of irradiation to be used will depend in part upon the underlying layers. For example, certain types of irradiation may degrade windings in a wound golf ball. On the other hand, balls with a solid core would not be subject to the same concerns. However, with any type of core, certain types of irradiation will tend to crosslink and thus harden the core. Depending upon whether this type of effect is sought or is to be avoided, the appropriate type of irradiation can be selected.

[0153] The level of radiation employed depends upon the desired end characteristics of the final game ball, e.g. golf ball, cover. However, generally a wide range of dosage levels may be used. For example, total dosages of up to about 12.5, or even 15 Mrads may be employed. Preferably, radiation delivery levels are controlled so that the game ball is not heated above about 80° C. (176° F.) while being crosslinked.

[0154] The layers of the cover may be formed from generally the same resin composition, or may be formed from different resin compositions with similar hardnesses. For example, one cover layer may be formed from an ionomeric resin of ethylene and methacrylic acid, while another layer is formed from an ionomer of ethylene and acrylic acid. One or more cover layers may contain polyamides or polyamide-nylon copolymers or intimate blends. Furthermore, polyurethanes, pebax, or thermosetting polyurethane can be used.

[0155] In order to visibly distinguish the layers, a wide variety of agents such as phosphorous, florescent dies, florescent pigments, etc. can be used.

[0156] Additional materials may also be added to the cover (or inner and outer cover layers) of the present invention as long as they do not substantially reduce the playability properties of the ball. Such materials include dyes (for example, Ultramarine Blue™ sold by Whitaker, Clark, and Daniels of South Plainsfield, N.J.) (see U.S. Pat. No. 4,679,795), optical brighteners, pigments such as titanium dioxide, zinc oxide, barium sulfate and zinc sulfate; UV absorbers; antioxidants; antistatic agents; and stabilizers. Moreover, the cover compositions of the present invention may also contain softening agents such as those disclosed in U.S. Pat. Nos. 5,312,857 and 5,306,760, both of which are herein incorporated by reference, including plasticizers, metal stearates, processing acids, etc., as long as the desired properties produced by the golf ball covers of the invention are not impaired.

[0157] Moreover, since there are various hues of white, i.e. blue white, yellow white, etc., trace amounts of blue pigment may be added to the cover stock composition to impart a blue white appearance thereto. However, if different hues of the color white are desired, different pigments can be added to the cover composition at the amounts necessary to produce the color desired.

[0158] In addition, it is within the purview of this invention to add to the cover compositions of this invention compatible materials such as antioxidants (i.e. Santonox® R), antistatic agents, stabilizers and processing aids. The cover compositions of the present invention may also contain softening agents, such as plasticizers, etc., and reinforcing materials such as glass fibers and inorganic fillers, as long as the desired properties produced by the golf ball covers of the invention are not impaired.

[0159] In one preferred form of the invention, the inner cover layer or inner cover layers contain filler materials. More particularly, filler materials are included in order to affect moment of inertia and spin of the golf ball, for example. Suitable filler materials for the inner cover layer or layers of the golf ball include, but are not limited to, clay, talc, asbestos, graphite, glass, mica, calcium metal silicate, barium sulfate, zinc sulfide, aluminum hydroxide, silicates, diatomaceous earth, carbonates such as calcium carbonate, magnesium carbonate and the like, metals such as titanium, tungsten, aluminum, bismuth, nickel, molybdenum, iron, copper, brass, boron, bronze, cobalt and beryllium, and alloys of the above metals, metal oxides such as zinc oxide, iron oxide, aluminum oxide, titanium oxide, magnesium oxide, zirconium oxide and the like, particulate synthetic plastic such as high molecular weight polyethylene, polystryene, polyethylene ionomer resins and the like, particulate carbonaceous materials such as carbon black, natural bitumen and the like, as well as cotton flock, cellulose flock, and leather fiber.

[0160] Dark colored fillers generally are not preferred for use at the outer surface of the ball if a white ball is desired. Thus, a two-layer cover in which a non-white filler is only present in the inner cover layer can be employed.

[0161] The amount of filler employed is primarily a function of weight restrictions. For example, weight may be removed from the core and placed in the inner and/or outer cover. This added weight will change the moment of inertia of the ball thereby potentially altering performance. Whereas typically the specific gravity of the cover layer or layers is about 0.95-1.00, it may be desirable to increase the specific gravity of one or more of the cover layers to greater than 1.0, preferably 1.1-2.0.

[0162] Furthermore, optical brighteners, such as those disclosed in U.S. Pat. No. 4,679,795, herein incorporated by reference, may also be included in the cover composition of the invention. Examples of suitable optical brighteners which can be used in accordance with this invention are Uvitex® OB as sold by the Ciba-Geigy Chemical Company, Ardsley, N.Y. Uvitex® OB thought to be 2,5-Bis(5-tert-butyl-2-benzoxazoyl)-thiophene. Examples of other optical brighteners suitable for use in accordance with this invention include Leucopure® EGM as sold by Sandoz, East Hanover, N.J. 07936. Leucopure® EGM is thought to be 7-(2n-naphthol(1,2-d)-triazol-2yl)3-phenyl-coumarin. Phorwhite® K-20G2 is sold by Mobay Chemical Corporation, P.O. Box 385, Union Metro Park, Union, N.J. 07083, and is thought to be a pyrazoline derivative. Eastobrite® OB-1 is 2,2′(1,2-ethenediyldi-4,1-phenylene)bisbenzoxazole and is available from Eastman Chemical Company.

[0163] Moreover, since many optical brighteners are colored, the percentage of optical brighteners utilized must not be excessive in order to prevent the optical brightener from functioning as a pigment or dye in its own right.

[0164] The percentage of optical brighteners which can be used in accordance with this invention is from about 0.01% to about 0.5% as based on the weight of the polymer used as a cover stock. A more preferred range is from about 0.05% to about 0.25% with the most preferred range from about 0.10% to about 0.20% depending on the optical properties of the particular optical brightener used and the polymeric environment in which it is a part.

[0165] Generally, the additives are admixed with an ionomer to be used in the cover composition to provide a masterbatch (M.B.) of desired concentration and an amount of the masterbatch sufficient to provide the desired amounts of additive is then admixed with the copolymer blends.

[0166] The above cover layer compositions, when combined with soft cores at the cover layer thicknesses described herein, produce golf balls having a relatively low spin in combination with good click and feel.

[0167] The cover compositions and molded balls of the present invention may be produced according to conventional melt blending procedures. In this regard, the ionomeric resins are blended along with the masterbatch containing the desired additives in a Banbury® type mixer, two-roll mill, or extruded prior to molding. The blended composition is then formed into slabs or pellets, etc. and maintained in such a state until molding is desired. Alternatively a simple dry blend of the pelletized or granulated resins and color masterbatch may be prepared and fed directly into the injection molding machine where homogenization occurs in the mixing section of the barrel prior to injection into the mold. Additives such as the fillers, etc., are added and uniformly mixed before initiation of the molding process.

[0168] The golf balls of the present invention can be produced by molding processes currently well known in the golf ball art. Specifically, the golf balls can be produced by conventional molding techniques, such as by injection molding or compression molding the novel cover compositions over the soft polybutadiene cores to produce a golf ball having a diameter of about 1.680 inches or greater, preferably at least 1.70 inches, and weighing about 1.620 ounces. Larger molds are utilized to produce the thicker covered oversized golf balls. For injection-molded cover layers having a thickness of up to about 3.0 mm, it may be preferable to mold the cover in a single step. For covers and for cover layers of 3.0 mm or more, it generally is preferable for reasons of both processability and uniformity to mold the cover in two layers. In compression molding, it may be appropriate to mold a thicker cover in a single layer. In compression molding, the cover composition is formed via injection at about 380° F. to about 450° F. into smooth surfaced hemispherical shells which are then positioned around the core in a dimpled golf ball mold and subjected to compression molding at 200 to 300° F. for 2 to 10 minutes, followed by cooling at 50 to about 70° F. for 2 to 10 minutes, to fuse the shells together to form an unitary ball. In addition, the golf balls may be produced by injection molding, wherein the cover composition is injected directly around the core placed in the center of a golf ball mold for a period of time at a mold temperature of from 50 to about 100° F. After molding the golf balls produced may undergo various further finishing steps such as flash trimming, priming, marking, finish coating and the like as is well known and is disclosed, for example in U.S. Pat. No. 4,911,451, herein incorporated by reference.

[0169] A preferred method of forming a golf ball according to the present invention is forming one or more layers via a fast-chemical-reaction process.

[0170] Specifically, the preferred method of forming a fast-chemical-reaction-produced component for a golf ball according to the invention is by reaction injection molding (“RIM”). RIM is a process by which highly reactive liquids are injected into a closed mold, mixed usually by impingement and/or mechanical mixing in an in-line device such as a “peanut mixer,” where they polymerize primarily in the mold to form a coherent, one-piece molded article. The RIM process usually involves a rapid reaction between one or more reactive components such as polyether= or polyester-polyol, polyamine, or other material with an active hydrogen, and one or more isocyanate-containing constituents, often in the presence of a catalyst. The constituents are stored in separate tanks prior to molding and may be first mixed in a mix head upstream of a mold and then injected into the mold. The liquid streams are metered in the desired weight to weight ratio and fed into an impingement mix head, with mixing occurring under high pressure, e.g., 1,500 to 3,000 psi. The liquid streams impinge upon each other in the mixing chamber of the mix head and the mixture is injected into the mold. One of the liquid streams typically contains a catalyst for the reaction. The constituents react rapidly after mixing to gel and form polyurethane polymers. Polyureas, epoxies, and various unsaturated polyesters also can be molded by RIM.

[0171] RIM differs from non-reaction injection molding in a number of ways. The main distinction is that in RIM a chemical reaction takes place in the mold to transform a monomer or adducts to polymers and the components are in liquid form. Thus, a RIM mold need not be made to withstand the pressures which occur in a conventional injection molding. In contrast, injection molding is conducted at high molding pressures in the mold cavity by melting a solid resin and conveying it into a mold, with the molten resin often being at about 150 to about 350° C. At this elevated temperature, the viscosity of the molten resin usually is in the range of about 50,000 to about 1,000,000 centipoise, and is typically around 200,000 centipoise. In an injection molding process, the solidification of the resins occurs after about 10 to about 90 seconds, depending upon the size of the molded product, the temperature and heat transfer conditions, and the hardness of the injection molded material. Subsequently, the molded product is removed from the mold. There is no significant chemical reaction taking place in an injection molding process when the thermoplastic resin is introduced into the mold. In contrast, in a RIM process, the chemical reaction causes the material to set in less than about 5 minutes, often in less than 2 minutes, preferably in less than one minute, more preferably in less than 30 seconds, and in many cases in about 10 seconds or less.

[0172] If plastic products are produced by combining components that are preformed to some extent, subsequent failure can occur at a location on the cover which is along the seam or parting line of the mold. Failure can occur at this location because this interfacial region is intrinsically different from the remainder of the cover layer and can be weaker or more stressed. The present invention is believed to provide for improved durability of a golf ball cover layer by providing a uniform or “seamless” cover in which the properties of the cover material in the region along the parting line are generally the same as the properties of the cover material at other locations on the cover, including at the poles. The improvement in durability is believed to be a result of the fact that the reaction mixture is distributed uniformly into a closed mold. This uniform distribution of the injected materials eliminates knit-lines and other molding deficiencies which can be caused by temperature difference and/or reaction difference in the injected materials. The process of the invention results in generally uniform molecular structure, density and stress distribution as compared to conventional injection-molding processes.

[0173] The RIM process used in forming components of a multi-layered golf ball disclosed herein is substantially different from, and advantageous over, the conventional injection and compression molding techniques.

[0174] First, during the RIM process of the present application, the chemical reaction, i.e., the mixture of isocyanate from the isocyanate tank and polyol from the polyol tank, occurs during the molding process. Specifically, the mixing of the reactants occurs in the recirculation mix head and the after mixer, both of which are connected directly to the injection mold. The reactants are simultaneously mixed and injected into the mold, forming the desired component.

[0175] Typically, prior art techniques utilize mixing of reactants to occur before the molding process. Mixing under either compression or injection molding occurs in a mixer that is not connected to the molding apparatus. Thus, the reactants must first be mixed in a mixer separate from the molding apparatus, then added into the apparatus. Such a process causes the mixed reactants to first solidify, then later melt in order to properly mold.

[0176] Second, the RIM process requires lower temperatures and pressures during molding than does injection or compression molding. Under the RIM process, the molding temperature is maintained at about 100° F. to about 120° F. in order to ensure proper injection viscosity. Compression molding is typically completed at a higher molding temperature of about 320° F. (160° C.). Injection molding is completed at even a higher temperature range of from about 392° F. to about 482° F. (200 to 250° C.). Molding at a lower temperature is beneficial when, for example, the cover is molded over a very soft core so that the very soft core does not melt or decompose during the molding process.

[0177] Third, the RIM process creates more favorable durability properties in a golf ball than does conventional injection or compression molding. The preferred process of the present invention provides improved durability for a golf ball cover by providing a uniform or “seamless” cover in which the properties of the cover material in the region along the parting line are generally the same as the properties of the cover material at other locations on the cover, including at the poles. The improvement in durability is due to the fact that the reaction mixture is distributed uniformly into a closed mold. This uniform distribution of the injected materials eliminates knit-lines and other molding deficiencies which can be caused by temperature difference and/or reaction difference in the injected materials. The RIM process of the present invention results in generally uniform molecular structure, density and stress distribution as compared to conventional injection molding processes, where failure along the parting line or seam of the mold can occur because the interfacial region is intrinsically different from the remainder of the cover layer and, thus, can be weaker or more stressed.

[0178] Fourth, the RIM process is relatively faster than the conventional injection and compression molding techniques. In the RIM process, the chemical reaction takes place in under 5 minutes, typically in less than two minutes, preferably in under one minute and, in many cases, in about 30 seconds or less. The demolding time of the present application is 10 minutes or less. The molding process alone for the conventional methods typically takes about 15 minutes. Thus, the overall speed of the RIM process makes it advantageous over the injection and compression molding methods.

[0179] The present invention is further illustrated by the following examples in which the parts of the specific ingredients are by weight (pbw). It is to be understood that the present invention is not limited to the examples, and various changes and modifications may be made in the invention without departing from the spirit and scope thereof.

EXAMPLES Example 1 Thick, Single Cover Oversize Balls

[0180] A number of golf ball cores having Formulation A, shown below, were prepared. Core Formulation A Parts by Material Weight SMR-CV 60¹ 25.00 Taktene ® 220² 73.50 Hi-Sil ™ 234 LD³ 6.00 Zinc Oxide⁴ 5.00 Barytes #22⁵ 80.00 Stearic Acid⁶ 1.60 Agerite Superlite ™⁷ 1.60 TiO₂ Rutile 2020⁸ 3.00 Circolite ™ Oil⁹ 5.00 Red pigment¹⁰ 3.00 Sulfur (insol)¹¹ 3.14 Santocure ™ N.S.¹² 1.28 Methyl Zimate¹³ 0.27 D.P.G.¹⁴ 0.68 206.07

[0181] One to two dozen cores were made having an average diameter of 36.3 mm (1.430 inches) (Example 1-1). One to two dozen cores having an average diameter of 37.3 mm (1.470 inches) also were made (Example 1-2). The 36.3 mm diameter cores were cured at 320° F. for 12 minutes, followed by six minutes of cooling using cold water. The cores having a 37.3 mm diameter were cured at 320° F. for 12 minutes, followed by six minutes of cooling using cold water.

[0182] The cores were covered with a thick, single layer of an ionomeric cover material to produce an unfinished golf ball 43.7 mm (1.72 inches) in diameter. The ionomeric cover material consisted of Cover Formulation W, shown below: Cover Formulation W Parts by weight White Masterbatch - Parts by weight Iotek ® 8000 70.6 Iotek ® 7030 100. Iotek ® 7010 19.9 Unitane ® 0-110 31.72 White MasterBatch 9.5 Ultra Marine Blue ™ 0.6 Eastobrite ® OB-1 0.35 Santonox ® R 0.05

[0183] As shown in Table 9 below, the golf balls with a 36.3 mm average core diameter had an overall average weight of 43.5 grams, an average cover thickness of 3.68 mm (0.145 inches), an average PGA compression of 78, and an average coefficient of restitution (C.O.R.) of 0.744 (Example 1-1). The golf balls with 37.3 mm (1.470 inch) average core diameters had an average weight of 44.4 grams, an average cover thickness of 3.18 mm (0.125 inches), an average PGA compression of 48, and an average coefficient of restitution of 0.732 (Example 1-2). These thick covered, two piece oversized golf balls have excellent feel due to the combination of a hard cover and a very soft core, and could be used (due to their low average C.O.R.'s) as restricted flight golf balls.

[0184] A number of golf ball cores having Core Formulation B, shown below, were formed. Core Formulation B Parts by Material Weight Cariflex ® BR-1220¹ 67.35 Taktene ® 220² 27.50 Natsyn ™ 2200³ 5.15 Zinc Oxide⁴ 6.53 Limestone⁵ 8.25 Poly Pro ™ 20 Mesh⁶ 6.19 Regrind⁷ 19.59 Zinc Stearate⁸ 14.78 Zinc Diacrylate⁹ 19.24 Luperco ® 230XL or Trigonox ® 17/40¹⁰ 1.48

[0185] The cores were cured for 15 minutes at 310° F. followed by 7 minutes of cooling using cooling water. Cores having average diameters of 36.3 mm (1.430 inches) (Example 1-4) and of 37.3 mm (1.470 inches) were formed (Example 1-3).

[0186] Cores having an average diameter of 39.2 mm (1.545 inches) also were formed (Example 1-C1) as a control. These cores are representative of the size of cores in standard size, oversized golf balls.

[0187] The cores of Examples 1-3, 1-4 and 1-C1 were covered with a single layer of the same ionomeric cover material as was used in Examples 1-1 and 1-2. The 36.3 mm and 37.3 mm diameter cores resulted in thick covered, oversized golf balls having an overall diameter of 43.7 mm (1.72 inches) (Examples 1-3 and 1-4). Similarly, the 39.2 mm cores were used to form golf balls having a diameter of 43.8 mm (1.725 inches) (Example 1-C1).

[0188] The golf balls made from 36.3 mm cores (Example 1-4) had a final weight of 44.5 grams, a cover thickness of 3.68 mm (0.145 inches), a PGA compression of 112 and a coefficient of restitution of 0.811. The balls made from 37.3 mm cores (Example 1-3) had a weight of 45.1 grams, a cover thickness of 3.18 mm (0.124 inches), a PGA compression of 105, and a coefficient of restitution of 0.809. The normal cover thickness control balls having 39.2 mm cores (Example 1-C1) had an overall weight of 46.0 grams, a cover thickness of 2.29 mm (0.090 inches), a PGA compression of 93, and a coefficient of restitution of 0.812.

Example 2 Thick Covered Multi-Layer Golf Balls, Standard Size

[0189] A number of 32.8 mm (1.29 inch) average diameter golf ball cores were made using Core Formulation C, shown below. The curing process was the same as the sulfur curing process described above in Example 1. The cores were used to make four different types of golf balls having the cover compositions and thicknesses shown in Table 9 as Examples 2-1 to 2-4. The lotek® 959/960 cover formulation (Cover Formulation X utilized) also is shown below. Core Formulation C Cover Formulation X Parts by Parts by Weight Weight Cariflex ® BR 1220 80 Iotek ® 959 45.3 SMR CV 60 20 Iotek ® 960 45.3 Zinc Oxide 5 White MasterBatch 9.4 Limestone 110 (see formulation in Ex. 1) Stearic Acid 1.6 Agerite Superlite ™ 1.6 Circolite ™ Oil 5 Sulfur 3.14 Santocure ® N.S. 1.28 Methyl Zimate 0.28 D.P.G. 0.68 228.58

[0190] The resulting average PGA compression and coefficient of restitution of the golf balls also is shown in Table 9. A control example using a standard size, two piece ball core, i.e. 39.2 mm (1.545 inch) core, having Core Formulation I, shown below, and a single cover layer with a thickness of 1.78 mm (0.070 inches) also was formed. The physical properties of the resulting balls are shown in Table 9 as 2-C1. Core Formulation I Parts by Weight Cariflex ® BR-1220 70.80 Taktene ® 220 29.20 Zinc Oxide 6.93 Limestone 18.98 Poly Pro ™ 20 Mesh 2.55 Regrind 20.07 Zinc Stearate 20.07 ZDA 30.29 Blue masterbatch 0.01 Luperco ® 231-XL or Trigonox ® 29/40² 0.90

[0191] The very thick covered balls (2-1 to 2-4) had the same, or substantially the same, overall compression (i.e. 105-116 PGA) as the thin covered control (i.e., 2-C1, 105 PGA) even though the thick covers were more than double, and in some instances nearly triple, the thickness of the control.

Example 3 Thick Covered Multi-Layer Balls, Standard Size

[0192] A number of sulfur-cured golf ball cores having an average diameter of 32.5 mm (1.28 inches) and the formulation shown below were formed: Core Fomulation D Materials phr Cariflex ® BR-1220 80 SMR CV-60 20 Zinc Oxide 5 Limestone 20 Stearic Acid 1.6 Circolite ™ oil 5 Sulfur 3.14 Santocure ™ N.S. 1.28 Methyl Zimate 0.28 D.P.G. 0.68 Agerite White ™¹ 0.8

[0193] The cores were cured for 12 minutes at 320° F., followed by cooling for six minutes with cooling water. The sulfur-cured cores (Examples 3-3, 3-4, 3-7 and 3-8) had an average surface Shore A hardness of 71, an average surface Shore C hardness of 35 and an average surface Shore D hardness of 21.

[0194] A number of peroxide-cured cores having an average diameter of 32.5 mm (1.28 inches) and Core Formulation B, shown above were formed. The cores were cured for 15 minutes at 310° F., followed by cooling for seven minutes using cooling water. The cores (Examples 3-1, 3-2, 3-5 and 3-6) had the PGA compression and COR values shown in Table 6.

[0195] A number of standard size “control” cores were made having a diameter of 39.2 mm (1.545 inches) and having Core Formulation F, shown below, were formed (Examples 3-C1 and 3-C2). Core Fomulation F Parts by Weight Cariflex ® BR-1220 70.37 Taktene ® 220 29.63 Zinc Oxide 6.67 Limestone 24.07 Poly Pro ™ 20 Mesh 8.89 Regrind 17.04 Zinc Stearate 18.52 Zinc Diacrylate 27.41 Luperco ® 231-XL or Trigonox ® 17/40 0.9

[0196] Furthermore, a number of “control” cores having a diameter of 39.2 mm (1.545 inches) and having Core Formulation G, shown below, were formed (Examples 3-C3 and 3-C4). Core Fomulation G Parts by Weight Cariflex ® BR-1220 73.33 Taktene ® 220 26.67 Zinc Oxide 22.33 Regrind 10 Zinc Stearate 20 Zinc Diacrylate 26 Luperco ® 231-XL or Trigonox ® 17/40 0.9

[0197] The 32.5 mm cores were covered with a thick multi-layer cover, i.e. 3.35 mm (0.132 inch) thick layer of ionomer followed by a 1.78 mm (0.070 inch) thick layer of the same or a different ionomer. The covers had a “422 tri” dimple pattern, which is the same dimple pattern as is used on the Top-Flite® Hot XL (1995), tour trajectory ball. The compression and coefficient of the cores, balls having the first cover layer, and balls having the second cover layer, as well as the finished balls, was obtained and is shown in Table 9. The control cores were covered with a single layer of ionomer having a thickness of 1.78 mm (0.070 inches).

[0198] The results demonstrate that thick covered multi-layer golf balls can be produced having comparable compression and C.O.R. values as existing multi-layer golf balls.

Example 4

[0199] A number of thermoplastic golf ball cores containing 100 parts by weight Exact® 4049 (Exxon Chemical Co.), a metallocene catalyzed polyolefin and 60 parts by weight of tungsten powder were formed (Core Formulation H, Examples 4-1, 4-2, 4-5 and 4-6). The cores were cured for 5 minutes at 320° F. followed by cooling using cooling water for 7 minutes. The cores had an average weight of 23.3 grams and an average diameter of 32.5 mm (1.28 inches). The cores were covered with a 3.35 mm (0.132 inch) thick layer of ionomer, followed by a second cover having a thickness of about 1.78 mm (0.070 inches). The inner and outer cover layers had the formulations Y and Z as shown in Table 9. Cover formulation Y is as follows: Cover Formulation Y Parts by Weight Iotek ® 1002 45.3 Iotek ® 1003 45.3 White MasterBatch  9.4 (see formulation in Ex. 1)

[0200] Cover Formulation Z is as follows: Cover Formulation Z Parts by Weight Iotek ® 8000 70.6 Iotek ® 7010 19.9 White MasterBatch  9.5 (see formulation in Ex. 1)

[0201] A number of crosslinked cores were made using 100 parts by weight of Exact® 4049 (Exxon Chemical Co., Houston, Tex.), which is a metallocene catalyzed polyolefin, 60 parts by weight of tungsten powder and 5 parts by weight Trigonox® 17/40 (Core Formulation J, Examples 4-3, 4-4 and 4-7). The cores were cured for 14 minutes at 320° F. followed by cooling with cooling water for 7 minutes. The cores had a weight of 23.6 grams. The cores had a diameter of 32.5 mm (1.28 inches), and were covered with the same types and thicknesses of cover materials as were used for the thermoplastic cores. The cover materials are shown in Table 9. The outer covers of Example 4 employed a “422 Hex” dimple pattern, which is the same dimple pattern as is used on the Top-Flite® XL (1996), regular trajectory ball.

[0202] The compression and coefficient values for the balls having a single cover layer, both cover layers, and finished products were determined and are shown in Table 9. As shown by the results, the thick covered balls, having metallocene catalyzed polyolefin cores, give relatively soft compression versus the thick covered balls having polybutadiene cores, and demonstrate the variety of properties which are possible with the novel constructions of the invention. The balls of this Example which have cores made of metallocene catalyzed polyolefin would be useful as range or practice balls, as they have a soft feel and high spin, as well as a very durable, hard cover. TABLE 9 CORE INNER COVER OUTER COVER FINISHED BALL COR Thick- COR Thick- COR COR SPIN EX. Size Comp (× ness Comp (× ness Comp (× Weight Comp (× Revs/ # Type¹ mm (PGA) 1000) Type² mm (PGA) 1000) Type² mm (PGA) 1000) (g) (PGA) 1000) min 1-1 A 36.32 — — W 3.68 43.50 78 744 — 1-2 A 37.34 — — W 3.18 44.40 48 732 — 1-3 B 37.34 — — W 3.18 45.10 105 809 — 1-4 B 36.32 — — W 3.68 44.50 112 811 — 1-C1 B 39.24 — — W 2.29 46.00 93 812 — 2-1 C 32.77 — — W 3.18 — — W 1.78 106 753 — 2-2 C 32.77 — — W 3.56 — — W 1.40 105 752 — 2-3 C 32.77 — — X 3.18 — — X 1.78 116 746 — 2-4 C 32.77 — — X 3.56 — — X 1.40 114 770 — 2-C1 I 39.24 — — — — — — W 1.78 105 803 — 3-1 B 32.51 71 759 X 3.35 115  786 X 1.78 122 791 130 806 6314 3-2 B 32.51 71 759 X 3.35 115  786 W 1.78 118 778 126 796 6095 3-3 D 32.51 X 3.35 75 768 X 1.78 110 769 117 790 — 3-4 D 32.51 X 3.35 75 768 W 1.78 102 764 114 778 — 3-5 B 32.51 71 759 W 3.35 110  772 X 1.78 120 788 128 801 — 3-6 B 32.51 71 759 W 3.35 110  772 W 1.78 118 775 126 791.00 — 3-7 D 32.51 W 3.35 69 749 X 1.78 108 771 116 776 7999 3-8 D 32.51 W 3.35 69 749 W 1.78 102 758 111 764 — 3-C1 F 39.24 98 752 — — — — X 1.78 105 790 108 797 — 3-C2 F 39.24 96 762 — — — — W 1.78 102 789 106 791 — 3-C3 G 39.24 87 767 — — — — X 1.78 98 800 102 807 — 3-C4 G 39.24 87 787 — — — — W 1.78 95 789 100 799 — 4-1 H 32.51 Y 3.35 79 731 Y 1.78 103 742 45.40 106 749 8497 4-2 H 32.51 Z 3.35 77 737 Y 1.78 101 746 45.30 105 753 8081 4-3 J 32.51 Y 3.35 80 740 Y 1.78 105 757 46.00 107 763 8337 4-4 J 32.51 Z 3.35 78 741 Y 1.78 103 759 46.20 105 763 8642 4-5 H 32.51 Y 3.35 79 731 Z 1.78 102 736 45.40 105 743 8226 4-6 H 32.51 Z 3.35 77 737 Z 1.78 99 747 45.20 103 751 8758 4-7 J 32.51 Z 3.35 78 741 Z 1.78 99 751 45.90 104 759 —

Example 5A

[0203] The balls of Examples 3-1, 3-2, 3-7, and 4-1 to 4-6 were spin tested under the following conditions:

[0204] Miyamae Driving Machine

[0205] Club: Top-Flite® Custom 9 iron

[0206] Club Head Speed: 105 fps

[0207] The results are shown in Table 6 above.

[0208] The balls of Examples 3-1, 3-2, 3-7, 4-5 and 4-6 were distance tested and were compared with the 1995 Top-Flite® Hot XL golf balls. The distance test conditions are provided below:

[0209] Club Name: Top-Flite Tour 10.5

[0210] Club Head Speed: 160 ft/sec

[0211] Launch Angle—degrees: 9.5

[0212] The distance test results are shown below in Table 10. TABLE 10 Flight Carry Time Carry Diff Ctr Dev¹ Roll Total Dist Total Diff Ball Traj deg. sec yds yds yds yds yds yds 3-1 12.50 10.00 244.40 0.00 −2.25 11.30 255.60 0.00 3-7 12.80 10.00 237.70 −6.60 −1.75 9.40 247.10 −8.50 3-2 12.10 10.00 227.40 −17.00 −3.04 19.20 246.60 −9.10 4-5 10.90 10.00 225.50 −18.90 −6.54 10.20 235.70 −20.00 4-6 11.30 9.90 226.80 −17.50 −6.71 11.70 238.50 −17.10 Hot XL 11.70 10.00 237.80 −6.60 −4.75 13.10 250.90 −4.80 (1995)

[0213] The longest ball is that of Example 3-1. This result is surprising, particularly in view of the fact that this ball has a COR of 0.806, while the 1995 Top-Flite® Hot XL ball has a COR of 0.812±0.003. The ball of Example 3-2 also had a surprisingly long total distance given its low COR of 0.1796.

Example 5B

[0214] Distance tests were conducted for the balls of Examples 3-1, 3-2 and 4-1 to 4-4 under slightly different conditions, which were the following:

[0215] Club Name: Top-Flite® Tour 10.5

[0216] Club Head Speed: 155ft/sec

[0217] Launch Angle—degrees: 9.6

[0218] The distance test results are shown below in Table 11. TABLE 11 Flight Carry Time Carry Diff Ctr Dev Roll Total Dist Total Diff Ball Traj deg. sec yds yds yds yds yds yds 4-1 11.50 9.90 227.10 −12.20 2.08 13.10 240.20 −12.90 4-2 11.90 10.00 226.10 −13.10 1.96 13.40 239.50 −13.60 4-3 11.80 10.00 228.00 −11.30 2.54 12.10 240.10 −13.00 4-4 11.80 10.00 227.40 −11.90 0.63 11.10 238.50 −14.60 3-1 12.00 10.00 239.30 0.00 2.10 13.80 253.10 0.00 3-2 12.00 10.00 233.40 −5.90 2.79 11.10 244.50 −8.60 Hot XL 12.40 10.00 239.00 −0.20 2.46 13.80 252.90 −0.20 (1995)

[0219] Once again, the ball of Example 3-1 is the longest. The ball of Example 3-2 again had a surprisingly long total distance given its low COR.

Example 6

[0220] A number of standard size, control golf ball cores having an average diameter of 39.2 mm (1.545 inches) and a weight of 36.7 g were formed using Core Formulation K, shown below. Core Fomulation K Parts by Weight Cariflex ® 1220 70 Taktene ® 220 30 Zinc Oxide 6.7 Zinc diacrylate 27.4 Zinc Stearate 18.5 Limestone 24 Poly Pro ™ 20 Mesh 8.9 Regrind 17 Trigonox ® 17/40 0.9

[0221] The cores were cured for 11½ minutes at 320° F., and were then cooled using cooling water for about 7 minutes. The cores had a PGA compression of 95 and a COR of 0.770.

[0222] A number of golf ball cores having Core Formulation L (shown below) and average diameters of 34.8 mm (1.37 inches) and 39.9 mm (1.57 inches) were formed. The cores were cured for 12 minutes at 320° F., followed by cooling using cooling water for about 6 minutes. Core Formulation L Parts by Weight Cariflex ® 1220 100 Stearic Acid 2 Zinc Oxide 4 Barytes 52 Hi-Sil ™ 233¹ 7.5 Vanox ™ 1290² 1 Sulfur 5.25 Durax ™³ 1.75 DOTG⁴ 1 Bismate ™⁵ 2.8

[0223] The cores of control Examples 6-C1, 6-C2 and 6-C3 were covered with a single cover layer having a thickness of 1.78 mm (0.07 inches). The control cores were covered with the cover formulations shown in Table 12, which are the same as cover formulations W-Z in Examples 1-4. The cores of Examples 6-1 through 6-10 were covered with inner and outer covers having the cover formulations and thicknesses shown in Table 12. All of the balls of the present invention and the control balls were distance tested using a 5-iron at 128 feet per second and a driver at 160 feet per second.

[0224] As shown in Table 12, while the thick covered balls of the present invention had substantially lower coefficients of restitution than the control balls, their distance was only slightly shorter. Thus, the golf balls of the invention provide a greater distance per point of COR as compared to the control balls. TABLE 12 Inner Cover Outer Cover 5 Iron @ Driver @ Thick- Thick- Finished Ball 128 fps 160 fps Core Dia. ness Wgt. PGA COR × ness Wgt. PGA COR × Carry Total Carry Total Ex. # Type Material mm mm g Comp 1000 Material mm g Comp 1000 yds yds yds yds 6-C1 K N.A. N.A. N.A. N.A. N.A. N.A. Z 1.78 45.40 104 792 170 172 249 256 6-1 L W 39.20 3.50 35.80 70 742 Z 1.78 44.60 105 764 167 170 242 248 6-2 L Y 39.20 3.50 35.80 74 744 Z 1.78 44.80 108 759 166 168 241 246 6-3 L X 39.20 3.50 36.30 88 766 Z 1.78 45.00 114 771 Not Not Tested Tested 6-4 L W 39.90 3.81 37.10 77 748 Y 1.40 45.00 107 766 164 167 242 247 6-5 L Y 39.90 3.81 37.20 82 756 Y 1.40 45.00 109 765 165 169 243 247 6-6 L W 39.20 3.50 35.80 70 742 Y 1.78 44.90 107 757 166 167 243 247 6-C2 K N.A. N.A. N.A. N.A. N.A. N.A. Y 1.78 45.70 106 804 167 171 251 256 6-C3 K N.A. N.A. N.A. N.A. N.A. N.A. X 1.78 45.80 109 807 168 174 252 257 6-7 L Y 39.20 3.50 35.80 78 744 X 1.78 45.20 111 779 169 171 245 250 6-8 L X 39.20 3.50 36.30 88 766 X 1.78 45.40 116 783 170 170 244 249 6-9 L W 39.90 3.81 37.10 77 748 X 1.40 45.30 112 772 171 171 242 248 6-10 L X 39.90 3.81 37.50 92 768 X 1.40 45.20 118 774 172 172 245 250

[0225] The foregoing description is, at present, considered to describe the preferred embodiments of the present invention. However, it is contemplated that various changes and modifications apparent to those skilled in the art, may be made without departing from the present invention. Therefore, the foregoing description is intended to cover all such changes and modifications encompassed within the spirit and scope of the present invention, including all equivalent aspects. 

We claim:
 1. A golf ball comprising: a core; a first cover layer disposed about said core, said first cover layer comprising a majority proportion by weight of a composition selected from the group consisting of polyurethane, polyureas and blends thereof, said first cover layer exhibiting a Shore D hardness of less than 60; and a second outermost cover layer disposed on said first cover layer, said second cover layer comprising a majority proportion by weight of a polyurethane, said second cover layer exhibiting a Shore D hardness of less than
 60. 2. The golf ball of claim 1 wherein said first cover layer and said second cover layer each exhibit a Shore D hardness less than
 55. 3. The golf ball of claim 2 wherein said first cover layer and said second cover layer each exhibit a Shore D hardness less than
 50. 4. The golf ball of claim 1 wherein said core exhibits a PGA compression of from 20 to
 85. 5. The golf ball of claim 4 wherein said core exhibits a PGA compression of from 40 to
 60. 6. The golf ball of claim 1 wherein said polyurethane is the product of a polyisocyanate and a polyol.
 7. The golf ball of claim 6 wherein said polyisocyanate is selected from the group consisting of diphenylmethane diisocyanate, hexamethylene diisocyanate, cyclohexane diisocyanate, toluene diisocyanate, bitolylene diisocyanate, p-phenylene diisocyanate, dicyclohexylmethane diisocyanate, 3-isocyanato-methyl-3,5,5-trimethylcyclo-hexyl isocyanate, trans-cyclohexane-1,4-diisocyanate, m-tetramethyl-xylylene, 1,5-naphthalene diisocyanate, polymethylene polyphenyl isocyanate and combinations thereof.
 8. The golf ball of claim 6 wherein said polyol is selected from the group consisting of polyester polyol, polyether polyol, and combinations thereof.
 9. The golf ball of claim 1 wherein said polyurethane is a thermoset.
 10. The golf ball of claim 1 wherein said polyurethane is a thermoplastic.
 11. The golf ball of claim 1 further comprising a third cover layer disposed between said first cover layer and said second cover layer.
 12. The golf ball of claim 1 wherein the difference between the Shore D hardness of said first layer and the Shore D hardness of said second layer is less than
 5. 13. The golf ball of claim 1 wherein the difference between the Shore D hardness of said first layer and the Shore D hardness of said second layer is less than
 2. 14. A golf ball comprising: a core; a first cover layer disposed about said core, said first cover layer comprising a majority proportion by weight of a composition selected from the group consisting of polyurethane, polyureas and blends thereof, said first cover layer exhibiting a Shore D hardness less than 60; and a second outermost cover layer disposed on said first cover layer, said second cover layer exhibiting a Shore D hardness of less than
 60. 15. The golf ball of claim 14 wherein said first cover layer and said second cover layer each exhibit a Shore D hardness less than
 55. 16. The golf ball of claim 15 wherein said first cover layer and said second cover layer each exhibit a Shore D hardness less than
 50. 17. The golf ball of claim 14 wherein said core exhibits a PGA compression of from 20 to
 85. 18. The golf ball of claim 17 wherein said core exhibits a PGA compression of from 40 to
 60. 19. The golf ball of claim 14 wherein said polyurethane is the product of a polyisocyanate and a polyol.
 20. The golf ball of claim 19 wherein said polyisocyanate is selected from the group consisting of diphenylmethane diisocyanate, hexamethylene diisocyanate, cyclohexane diisocyanate, toluene diisocyanate, bitolylene diisocyanate, p-phenylene diisocyanate, dicyclohexylmethane diisocyanate, 3-isocyanato-methyl-3,5,5-trimethylcyclo-hexyl isocyanate, trans-cyclohexane-1,4-diisocyanate, m-tetramethyl-xylylene, 1,5-naphthalene diisocyanate, polymethylene polyphenyl isocyanate and combinations thereof.
 21. The golf ball of claim 19 wherein said polyol is selected from the group consisting of polyester polyol, polyether polyol, and combinations thereof.
 22. The golf ball of claim 14 wherein said polyurethane is a thermoset.
 23. The golf ball of claim 14 wherein said polyurethane is a thermoplastic.
 24. The golf ball of claim 14 further comprising a third cover layer disposed between said first cover layer and said second cover layer.
 25. The golf ball of claim 14 wherein the difference between the Shore D hardness of said first layer and the Shore D hardness of said second layer is less than
 5. 26. The golf ball of claim 14 wherein the difference between the Shore D hardness of said first layer and the Shore D hardness of said second layer is less than
 2. 27. A golf ball comprising: a core; a first cover layer disposed on said core, said first cover layer exhibiting a Shore D hardness of less than 60; and a second outermost cover layer disposed on said first cover layer, said second cover layer comprising a majority proportion by weight of a composition selected from the group consisting of polyurethane, polyureas and blends thereof, said second cover layer exhibiting a Shore D hardness of less than
 60. 28. The golf ball of claim 27 wherein said first cover layer and said second cover layer each exhibit a Shore D hardness less than
 55. 29. The golf ball of claim 28 wherein said first cover layer and said second cover layer each exhibit a Shore D hardness less than
 50. 30. The golf ball of claim 27 wherein said core exhibits a PGA compression of from 20 to
 85. 31. The golf ball of claim 30 wherein said core exhibits a PGA compression of from 40 to
 60. 32. The golf ball of claim 27 wherein said polyurethane is the product of a polyisocyanate and a polyol.
 33. The golf ball of claim 32 wherein said polyisocyanate is selected from the group consisting of diphenylmethane diisocyanate, hexamethylene diisocyanate, cyclohexane diisocyanate, toluene diisocyanate, and combinations thereof.
 34. The golf ball of claim 32 wherein said polyol is selected from the group consisting of polyester polyol, polyether polyol, and combinations thereof.
 35. The golf ball of claim 27 wherein said polyurethane is a thermoset.
 36. The golf ball of claim 27 wherein said polyurethane is a thermoplastic.
 37. The golf ball of claim 27 further comprising a third cover layer disposed between said first cover layer and said second cover layer.
 38. The golf ball of claim 27 wherein the difference between the Shore D hardness of said first layer and the Shore D hardness of said second layer is less than
 5. 39. The golf ball of claim 27 wherein the difference between the Shore D hardness of said first layer and the Shore D hardness of said second layer is less than
 2. 